Electronic camera that synthesizes two images taken under different exposures

ABSTRACT

Disclosed herein is an electronic camera for generating an image having a wide dynamic range by synthesizing two image pickup signals of different exposure amount generated by using an electronic shutter function and means for shutting off light, shading of image pickup signals resulting from difference in charge accumulating time among the pixels of image pickup device due to operation from opened state to closed state of the means for shutting off light being corrected by a shading correction means to form a synthesized image without an occurrence of false color due to shading. Also provided is an electronic camera generating two image pickup signals of different exposure amount by two shots of picture taking each using a flash emission in combination, at least one of an electronic shutter of image pickup device and means for shutting off light, as well as an emission of the flash emission means, being controlled to equalize between the two shots of picture taking ratio of exposure by normal light excluding light from the flash emission means and ratio of emission amount by the light from the flash emission means so that the two image pickup signals can be readily generated as having a predetermined exposure amount ratio in every part of a frame of picture even when a flash emission is used in combination.

BACKGROUND OF THE INVENTION

The present invention relates to electronic cameras (commonly called asdigital still camera) in which a plurality of image pickup signals ofdifferent exposure amount read out from a single image pickup device aresynthesized to obtain an image having a wide dynamic range.

Although solid-state image pickup devices such as CCD image pickupdevice are used in such image pickup apparatus as TV camera, videocamera, electronic camera, etc., there is a problem that the dynamicrange of a solid-state image pickup device is much narrower than that ofa silver salt photographic film.

To eliminate this problem, there have been proposed techniques in whichan image having an increased dynamic range is obtained by synthesizingtwo image pickup signals of different exposure amount read out from asingle image pickup device. For example, Japanese patent applicationlaid open No.4-207581 discloses those constructed as follows.

In particular, one of those disclosed therein comprises an image pickupdevice including a light receiving section having a plurality of lightreceiving elements for photoelectric conversion of optical informationand a means for transferring signals from the light receiving section.Immediately after performing a first exposure at the light receivingsection and transmitting signals of the first exposure to the transfermeans, a second exposure having a longer exposure time than the firstexposure is started. After outputting signals of the first exposure fromthe image pickup device, signals of the second exposure are transmittedto the transfer means to output signals of the second exposure from theimage pickup device. The second exposure is thereby performed in theperiod during which signals of the first exposure are outputted from theimage pickup device so as to make smaller a temporal difference inpicture taking caused by such plurality of times of exposure. In thisaspect, a disclosure is also made with respect to one in which the firstexposure time is controlled by transmitting of signals due to theexposure from the light receiving section to the transfer means, i.e.,by an electronic shutter function, while the second exposure time iscontrolled by a means for shutting off light to control an exposure timeof the image pickup device. The second exposure time can thus becontrolled independently from the transferring operation of the firstexposure signals.

Further, one as shown in FIG. 1 is disclosed in Japanese patentapplication laid open No.6-141229 as a construction for synthesizing twoimage pickup signals that are different in exposure amount to synthesizean image having a wide dynamic range. In particular, signals with ashorter charge accumulating period CS1 read out from CCD 501 arerecorded at memory 502, and the recorded signals are read out from thememory 502 at substantially the same timing as readout from CCD 501 ofsignals with a longer charge accumulating period CL1. The signals readout from the memory 502 are multiplied by CL1/CS1 for example “4” usinga multiplier 503. By this multiplication using such factor, signallevels of those signals differing from each other in charge accumulatingperiod with respect to the same object are theoretically brought to thesame level.

Next, a level weighting means H 505 assigns a weight corresponding tosignal level to the signal of charge accumulating period CS1 from themultiplier 503. A weight is assigned also to the signal of chargeaccumulating period CL1 at a level weighting means L 504. Thecharacteristics of the respective weights are shown in FIG. 2 whereabscissa represents an input signal level and ordinate represents aweighting factor to be assigned to the signals. The level weight L is aweight of 1 for input levels up to 80%, is linearly lowered in weightvalue for 80% to 100% and puts the weighting factor to 0 at the inputlevel of 100%. The level weight H, on the other hand, is a weight of 0for levels up to 80%, is linearly increased in weight value for 80% to100% and puts the weighting factor to 1 at the input level of 100%. Theweighting factor is always 1 for input levels of 100% and above. Theimage signals differing from each other in dynamic range are weightedthus and are synthesized as added together at an adder 506 to form asingle piece of image. The portions in good conditions (with favorableS/N and without saturation) are extracted through this weighting processto synthesize an image having a wide dynamic range. Since thesynthesized image is processed at a rate about twice the normal whensignals are read out from CCD 501, the scanning rate of signals isconverted at a rate converter 507 to ½ so that it corresponds to astandard TV signal. Further, while the signal level of the synthesizedimage at its maximum is 400%, the level is compressed to 100% at a levelcompression means 508. It should be noted that numeral 509 in FIG. 1denotes a timing control section.

In this manner, a difference in signal level due to difference in chargeaccumulating period is corrected with respect to the two signals thatare different in charge accumulating period. A larger weight is assignedto those portions where signals are not saturated while an adequate S/Nis kept to make a selection from these image signals and at the sametime to smoothly synthesize the two image signals. The signal obtainedas having a wide dynamic range and an increased signal amplitude is thenoutputted after compressed to a standard signal level. An image havingan increased dynamic range is thereby synthesized from the two imagesignals having been controlled with respect to their charge accumulatingperiods at CCD of which dynamic range is narrow.

Further, Japanese patent application laid open No.62-108678 discloses atechnique in which, when an image having a wide dynamic range is to beobtained by synthesizing two image pickup signals that are different inexposure amount, one of the image pickup signals is picked up by usingonly natural light while the other image pickup signal is generated by apicture taking process using a strobe light. These image pickup signalsare compared with each other and the portions of greater signal areoutputted to obtain a synthesized image.

Furthermore, a disclosure i s made in Japanese Patent PublicationNo.2659570 with respect to an electronic still camera in which, at thesame time of causing strobe light to emit for a plurality of times, aplurality of times of readout of charge are effected within a timeperiod for taking one frame of picture so that amount of light to bereceived is adjusted by control of an emission amount of strobe light oran electronic shutter operation of solid-state image pickup device so asto increase dynamic range without a saturation in output of thesolid-state image pickup device even in high luminance regions.

Referring now to the above Japanese patent application laid openNo.4-207581, it discloses a technique where, of two image pickup signalsthat are different in exposure amount, an image of smaller exposureamount is picked up first in time by using an electronic shutterfunction of the image pickup device and, then, an image of greaterexposure amount is picked up while controlling the charge accumulatingtime using a means for shutting off light (mechanical shutter). If,however, a means for shutting off light is employed in an electroniccamera, such means for shutting off light is normally kept in its openedstate. A charge accumulating time is controlled by a transition from theopened state to its closed state. In this case, therefore, the chargeaccumulating time differs from one position to another on the lightreceiving surface of the image pickup device. A shading thus results. Inthe disclosure of the above publication, however, this point is nottaken into consideration at all and a means for preventing a shading isnot mentioned either. There is another problem that, in respect ofcontrol of charge accumulating period, a means for shutting off light isnot very accurate when compared to an electronic shutter of the imagepickup device.

Furthermore, in the techniques disclosed in the above publications, anaccuracy is not taken into consideration in setting an exposure amountratio of two image pickup signals when the two image pickup signals ofdifferent exposure amount are to be obtained. The problems in the caseof using a flash emission means are not mentioned either.

In particular, if the luminance of the object of picture is at arelatively low level, picture taking is performed by using a strobelight in combination. In forming a synthesized image having a widedynamic range through a synthesis of two image pickup signals ofdifferent exposure amount, if an attempt is made to simply synthesizethe obtained two image pickup signals where one of the image pickupsignals is generated by using natural light alone and the other of theimage pickup signals by a strobe light in combination, it is difficultdue to the intrinsically large variance of a strobe light, even with aconstant exposure time, to attain a precise correspondence between thetwo image pickup signals in order to achieve a predetermined ratio oftheir exposure amounts. Further, in the case of using a strobe light,while image pickup signal having a predetermined exposure ratio inrelation to the image pickup signal picked up by natural light alone canbe obtained at the portions within a picture frame reached by the strobelight, image pickup signal in the portions not reached by the strobelight is of the same exposure amount as one picked up by natural lightalone. The predetermined exposure ratio cannot be obtained. Furthermore,in the case of synthesizing image pickup signal by natural light andimage pickup signal by a strobe light, since these are the image pickupsignals different from each other in white balance, there is a problemthat color balance is partially lost in the synthesis. Moreover, in thecase of image pickup apparatus such as an electronic camera including anexposure setting means (AE), a white balance setting means (WB), a gaincontrol means, a stop control means, etc., when two image pickup signalsof different exposure amount are synthesized to obtain an image having awide dynamic range, no consideration is taken as to how to achieve acorrespondence between them.

Further, while the above Japanese patent application laid openNo.6-141229 discloses a technique in which synthesis is smoothlyperformed while changing the weighting factor when two image pickupsignals of different exposure amount are synthesized to synthesize animage having a wide dynamic range, the problem of false color insynthesizing a color image is not considered and no disclosure is madewith respect to the problems in using a strobe.

SUMMARY OF THE INVENTION

To eliminate the above described problems of the conventional imagepickup apparatus in which a plurality of image pickup signals that aredifferent from each other in amount of exposure are synthesized to forman image having a wide dynamic range, it is a first object of thepresent invention to provide an electronic camera capable of correctingshading occurring in obtaining image pickup signal of a larger exposureamount by controlling charge accumulating time of image pickup deviceusing a means for shutting off light.

In accordance with the present invention, there is provided anelectronic camera including a single image pickup device having anelectronic shutter function capable of desirably controlling exposureamount by controlling charge accumulating time and means for shuttingoff light from a light receiving surface of the image pickup device.After generating an image pickup signal of smaller exposure amount byusing the electronic shutter function of the image pickup device, animage pickup signal of larger exposure amount is generated bycontrolling charge accumulating time of the image pickup device by themeans for shutting off light, the two image pickup signals beingsynthesized to obtain an image having an increased wide dynamic range.Control of charge accumulating time of the image pickup device by themeans for shutting off light is effected by operation from opened stateto closed state of the means for shutting off light. Shading correctionmeans is provided for correcting shading resulting from difference incharge accumulating time among the pixels of the image pickup deviceoccurring due to the operation toward closed state of the means forshutting off light.

By providing such shading correction means, it is possible to correctshading resulting from difference in charge accumulating time among thepixels from one position to another on the light receiving surface ofthe image pickup device due to the operation from opened state to closedstate of the means for shutting off light, so as to prevent anoccurrence of false color in the synthesized image. The above firstobject is thereby achieved.

It is another object of the present invention to provide an electroniccamera in which shading is not caused even when an image pickup signalis generated by effecting control of charge accumulating of the imagepickup device by the means for shutting off light.

In accordance with the present invention, there is provided anelectronic camera including a single image pickup device having anelectronic shutter function capable of desirably controlling exposureamount by controlling charge accumulating time and means for shuttingoff light from a light receiving surface of the image pickup device.After generating an image pickup signal of smaller exposure amount byusing the electronic shutter function of the image pickup device, animage pickup signal of larger exposure amount is generated bycontrolling charge accumulating time of the image pickup device by themeans for shutting off light, the two image pickup signals beingsynthesized to obtain an image having an increased wide dynamic range.The means for shutting off light is constituted by a focal-planeshutter. Shutter charge of the focal-plane shutter is effectedimmediately after a completion of electronic shutter's operation of theimage pickup device, in the state where charge accumulating operation ofthe image pickup device is halted. After completion of the shuttercharge, charge accumulating operation of the image pickup device isstarted such that control of the charge accumulating time is effected bya normal focal-plane shutter operation.

By thus using a focal-plane shutter as the means for shutting off lightand causing it to operate in the manner described above, no shadingoccurs in image pickup signal obtained by controlling chargeaccumulating time by means of the focal-plane shutter's operation.Accordingly, it is possible to obtain a synthesized image free fromshading without providing a shading correction means even when afocal-plane shutter is used. The above object is thereby achieved.

It is still another object of the present invention to provide anelectronic camera capable of accurately controlling charge accumulatingtime even when a charge accumulating time of image pickup device of arelatively long time period is to be controlled.

In accordance with the present invention, there is provided anelectronic camera including: a single image pickup device having anelectronic shutter function capable of desirably controlling exposureamount by controlling charge accumulating time; means for shutting offlight from a light receiving surface of the image pickup device; meansfor generating from the image pickup device two image pickup signals ofthe same object differing from each other in exposure amount; andsynthesizing means for obtaining an image having an increased widedynamic range by performing synthesis of the two image pickup signalsobtained by the means for generating image pickup signal. The means forgenerating image pickup signal is adapted to generate image pickupsignal of larger exposure amount by controlling charge accumulating timeof the image pickup device by the means for shutting off light aftergenerating image pickup signal of smaller exposure amount by using theelectronic shutter function of the image pickup device if chargeaccumulating time of the image pickup device for obtaining image pickupsignal of larger exposure amount is set as shorter than a periodrequired for readout of all the pixels of the image pickup device. Also,it is adapted to generate image pickup signal of larger exposure amountby using the electronic shutter function of the image pickup deviceinstead of the means for shutting off light, if charge accumulating timeof the image pickup device for obtaining image pickup signal of largerexposure amount is set as longer than the time period required forreadout of all the pixels of the image pickup device.

By constructing in this manner, an electronic shutter can be used insetting of charge accumulating time, if charge accumulating time of theimage pickup device for generating image pickup signal of largerexposure amount is set as longer than the time period required forreadout of all the pixels of the image pickup device. In such case,charge accumulating time can be accurately controlled by using theelectronic shutter which is more accurate than the means for shuttingoff light. The above object is thereby achieved.

It is yet another object of the present invention to provide anelectronic camera capable of accurately controlling exposure amounts ofimage pickup signals so as to attain an exposure amount ratiocorresponding to a previously set exposure amount ratio between twoshots of picture taking.

In accordance with the present invention, there is provided anelectronic camera having a function for performing synthesis of twoimage pickup signals obtained by performing by a single image pickupdevice two shots of picture taking of different exposure amount of thesame object to obtain an image having an increased wide dynamic range,further including a photometric device having a separate entity from theimage pickup device and means for setting charge accumulating time ofthe image pickup device at the second shot of picture taking so that itcorresponds to a previously set exposure amount ratio of the two shotsof picture taking based on an exposure amount measured by thephotometric device at the first shot of picture taking.

By thus setting charge accumulating time at the second shot of picturetaking based on an exposure amount at the first shot of picture takingmeasured by a photometric device, it is possible to accurately controlan exposure amount ratio between the two image pickup signals. The aboveobject is thereby achieved.

It is a further object of the present invention to provide an electroniccamera in which, when two image pickup signals of different exposureamount are generated by using flash emission means and are synthesizedto obtain an image having a wide dynamic range, time difference ingeneration of the two image pickup signals is reduced so as to obtainimages where difference due to the time difference in generation betweenthe two image pickup signals is relatively small.

In accordance with the present invention, there is provided anelectronic camera having a function for performing synthesis of twoimage pickup signals obtained by performing by a single image pickupdevice two shots of picture taking of different exposure amount of thesame object to obtain an image having an increased wide dynamic range,further including flash emission means. The flash emission means iscaused to emit at one or both of a timing in the second half of chargeaccumulating time of the image pickup device at the first shot ofpicture taking and a timing in the first half of charge accumulatingtime of the image pickup device at the second shot of picture taking.

By constructing in this manner, time difference of generation ingenerating two image pickup signals of different exposure amount byusing a flash emission means can be reduced so that images be obtainedas having a smaller difference due to time difference of generationbetween the two image pickup signals. The above object is therebyachieved.

In this aspect, it may further include a photometric device having aseparate entity from the image pickup device and means for causing theflash emission means to emit at both of the two shots of picture takingso as to set charge accumulating time of the image pickup device at thesecond shot of picture taking based on an emission amount ratio of thetwo emissions measured by the photometric device. By thus setting chargeaccumulating time of the second shot of picture taking based on anemission amount ratio of the two emissions measured by the photometricdevice, it is possible to accurately control an exposure amount ratio ofthe two image pickup signals even when flash emission means is used.

Also, in this aspect, the image pickup device may be provided with anelectronic shutter function capable of desirably controlling an exposureamount by controlling charge accumulating time. The flash emission meansis caused to emit at both of the two shots of picture taking and, at asmaller emission of the two emissions of the flash emission means,timing for stopping the smaller emission may be set as the same astiming for terminating an electronic shutter operation of the imagepickup device.

In general, proportion of surplus emission in a flash emission means islarger for a smaller flash emission amount. Accordingly, by setting asin the above the stop timing of smaller emission of the flash emissionmeans as the same as the ending timing of an electronic shutteroperation of the image pickup device, the smaller emission is notaffected by an surplus emission so that image pickup signals areobtained as having an accurate exposure amount ratio where an influenceof surplus emission in the case of using a flash emission means isreduced.

It is a further object of the present invention to provide an electroniccamera in which, when two image pickup signals of different exposureamount are synthesized to obtain an image having a wide dynamic range,the two image pickup signals are obtained as having the same depth offield.

In accordance with the present invention, there is provided anelectronic camera having a function by which two image pickup signalsobtained by performing by a single image pickup device two shots ofpicture taking of different exposure amount of the same object aresynthesized to obtain an image having an increased wide dynamic range,further including means for setting diaphragm stop value of lens fixedat the two shots of picture taking.

By thus performing the two shots of picture taking of different exposureamount with the diaphragm stop of lens being fixed by the lens diaphragmstop value fixing means, the two image pickup signals are obtained ashaving the same depth of field. The above object is thereby achieved.

In this aspect, exposure setting means may be provided such that adiaphragm stop value and/or shutter speed obtained by the exposuresetting means before taking picture be used at the picture taking forobtaining the image pickup signal of larger exposure amount and, at thepicture taking for obtaining the image pickup signal of smaller exposureamount, the same diaphragm stop value be used while shutter speed be setin such a manner as to correspond to a previously set exposure amountratio of the two shots of picture taking. It is also possible toconstruct the exposure setting means such that an exposure value be setbased on photometric output of a photometric device provided separatelyfrom the image pickup device or to construct the exposure setting meanssuch that an exposure value be set based on image pickup signal of theimage pickup device. By thus providing an exposure setting means andusing a diaphragm stop value obtained by the exposure setting means asfixed at the two shots of picture taking, it is possible to obtain imagepickup signals at an optimum exposure having the same depth of field.

It is a further object of the present invention to provide an electroniccamera in which, when two image pickup signals of different exposureamount are generated and synthesized to form an image having a widedynamic range, it is possible to obtain the synthesized image withoutproducing a false color due to difference in white balance.

In accordance with the present invention, there is provided anelectronic camera having a function by which two image pickup signalsobtained by performing by a single image pickup device two shots ofpicture taking of different exposure amount of the same object aresynthesized to obtain an image having an increased wide dynamic range,further including means for performing white balance correction bysetting the same white balance correction value for the two image pickupsignals of different exposure amount before the synthesis.

By thus providing white balance correction means to perform whitebalance correction by setting the same correction value for the twoimage pickup signals of different exposure amount before the synthesis,the synthesized image is obtained as having a wide dynamic range withoutproducing a false color due to difference in white balance. The aboveobject is thereby achieved.

In this aspect, white balance setting means may be provided such thatwhite balance correction value obtained by the white balance settingmeans before picture taking be used in white balance correction by thewhite balance correction means. By thus using a white balance correctionvalue obtained by the white balance setting means, it is possible toobtain the synthesized image even more accurately without producing afalse color due to difference in white balance.

Also, in this aspect, the correction value to be used in the whitebalance correction means may be set based on image pickup signal beforeperforming the synthesis. By thus setting a white balance correctionvalue based on the image pickup signal before performing the synthesis,the synthesized image can be obtained as even more accurately correctedof white balance.

Furthermore, in this aspect, the correction value to be used in thewhite balance correction means may be set based on the image pickupsignal of larger exposure amount of the two image pickup signals ofdifferent exposure amount before performing the synthesis. In general,while white balance correction is required to be performed for theportion to become an essential part of the object, the portion to becomean essential part is more likely to be included in the image pickupsignal of larger exposure amount. Accordingly, by setting white balancecorrection value based on the image pickup signal of larger exposureamount, a synthesized image of which white balance is corrected can beobtained efficiently.

It is a further object of the present invention to provide an electroniccamera in which a synthesized image having a wide dynamic range can beefficiently obtained without producing a false color due to differencein white balance.

In accordance with the present invention, there is provided anelectronic camera having a function by which two image pickup signalsobtained by performing by a single image pickup device two shots ofpicture taking of different exposure amount of the same object aresynthesized to obtain an image having an increased wide dynamic range,further including means for correcting white balance with respect to thesynthesized image having a wide dynamic range.

By thus correcting white balance with respect to the synthesized image,a synthesized image having a wide dynamic range can be efficientlyobtained without an occurrence of false color due to difference in whitebalance. The above object is thereby achieved.

In this aspect, white balance setting means may be provided such thatwhite balance correction value obtained by the white balance settingmeans before picture taking be used in white-balance correction by thewhite balance correction means. By thus using a white balance correctionvalue obtained by the white balance setting means, the synthesized imagecan be obtained efficiently and accurately without an occurrence offalse color due to difference in white balance.

Also, in this aspect, the correction value to be used in the whitebalance correction means may be set based on the synthesized imagehaving a wide dynamic range, or the correction value to be used in thewhite balance correction means may be set based on image pickup signalbefore performing the synthesis. By thus setting a white balancecorrection value, the synthesized image can be obtained as efficientlyand accurately corrected with respect to white balance.

Furthermore, in this aspect, the correction value to be used in thewhite balance correction means may be set based on the image pickupsignal of larger exposure amount of the two image pickup signals ofdifferent exposure amount before performing the synthesis. By thussetting white balance correction value based on the image pickup signalof larger exposure amount, a synthesized image having a wide dynamicrange can be obtained as more efficiently corrected with respect towhite balance.

It is a further object of the present invention to provide an electroniccamera in which, when two image pickup signals of different exposureamount are generated and synthesized to obtain an image having a widedynamic range, the two image pickup signals are readily generated assuitably corresponding at a high accuracy to a previously set exposureamount ratio.

In accordance with the present invention, there is provided anelectronic camera having a function by which two image pickup signalsobtained by performing by a single image pickup device two shots ofpicture taking of different exposure amount of the same object aresynthesized to obtain an image having an increased wide dynamic range,further including gain control means such that gain values at the gaincontrol means for the two image pickup signals are respectively set tovalues that are different from each other.

By thus setting the gain values corresponding to the respective imagepickup signals by the gain control means, it is possible to readilygenerate the two image pickup signals suitably corresponding to anexposure amount ratio at a high accuracy. The above object is therebyachieved.

In this aspect, the gain values for the two image pickup signals are setso that the exposure amount ratio of the two image pickup signalscorresponds to a previously set exposure amount ratio. By constructingin this manner, even when shutter speeds cannot accurately correspond toa previously set exposure amount ratio, the gain values can be adjustedto readily generate the two image pickup signals which accuratelycorrespond to the exposure amount ratio.

It is a further object of the present invention to provide an electroniccamera in which, when two image pickup signals of different exposureamount are synthesized to form an image having a wide dynamic range, thetwo image pickup signals of different exposure amount can be readilygenerated from an image pickup device by charge accumulating time of thesame duration.

In accordance with the present invention, there is provided anelectronic camera having a function by which two image pickup signalsobtained by performing by a single image pickup device two shots ofpicture taking of different exposure amount of the same object aresynthesized to obtain an image having an increased wide dynamic range,further including diaphragm control means such that the two image pickupsignals of different exposure amount are generated by changing diaphragmstop value of lens by the diaphragm control means.

By constructing in this manner, two image pickup signals of differentexposure amount can be readily generated by charge accumulating time ofthe same duration, thereby achieving the above object.

In this aspect, means for correcting peripheral attenuation of lens maybe provided such that correction with respect to peripheral attenuationwhich occurs as a result of difference in diaphragm stop value of lensbe performed for the two image pickup signals of different exposureamount generated by changing diaphragm stop value of lens by thediaphragm control means. When two image pickup signals of differentexposure amount are generated by changing diaphragm stop value of lensby the diaphragm control means, a difference in peripheral attenuationoccurs by different diaphragm stop values and a false color is producedin the synthesized image. However, a synthesized image without anoccurrence of false color resulting from a difference in peripheralattenuation can be obtained by correcting the difference in peripheralattenuation of lens by providing the means for correcting peripheralattenuation of lens in the above described manner.

Also, in this aspect, flash emission means may be provided such that twoimage pickup signals of different exposure amount be generated byeffecting flash emissions of the same emission amount and changing thediaphragm stop value of lens by the diaphragm stop value control meansat two shots of picture taking of different exposure amount. Byconstructing in this manner, it is not necessary to control flashemission amount and it becomes possible to equalize an exposure amountratio by flash emissions and an exposure amount ratio by ambient light.

It is a further object of the present invention to provide an electroniccamera in which, when a plurality of color image signals of differentexposure amount are synthesized to form a synthesized color image havinga wide dynamic range, the synthesized color image can be formed withoutproducing a false color or pseudo contour.

In accordance with the present invention, there is provided anelectronic camera having color image synthesizing means for forming acolor image having a wide dynamic range by synthesizing a plurality ofcolor image signals of different exposure amount, further includingweighting means for assigning weights to the plurality of color imagesignals corresponding to their respective signal level and means foradding the plurality of weighted color image signals such that theweighting means sets the same weighting factor respectively for eachcolor signal in the plurality of color image signals.

By thus effecting weighted addition by respectively setting the sameweighting factor to each color signal of the plurality of color imagesignals, a synthesized color image having a wide dynamic range can beformed without producing a false color or pseudo contour. The aboveobject is thereby achieved.

It is a further object of the present invention to provide an electroniccamera in which, even when flash emission is used, image pickup signalscan be readily generated as having a predetermined exposure amount ratioin every part in a frame of picture and a synthesized image having awide dynamic range can be obtained as preserving a uniform white balancein every part in the frame of picture.

In accordance with the present invention, there is provided anelectronic camera including: optical means for forming an optical imageof the object of picture taking; image pickup means for generating imagepickup signals by taking picture and effecting photoelectric conversionof an image of the object formed at the optical means; flash emissionmeans for illuminating the object; exposure condition designating meansfor designating exposure conditions at the image pickup means; imagepickup signal synthesizing means for synthesizing two image pickupsignals from two separate shots of picture taking at the image pickupmeans by exposure conditions designated by the exposure conditiondesignating means; flash emission control means for controlling emissionof the flash emission means in connection with the exposure conditionsfor each shot at the time of the two shots of picture taking; andcontrol means for controlling operation of each of the means in theabove.

By thus using flash emission for both of the two shots of picturetaking, it is possible to equalize an exposure amount ratio by normallight and an emission amount ratio by flash emission in every part in aframe of picture and it is also readily possible to make uniform whitebalance in the synthesized image. The above object is thereby achieved.

In one aspect of the present invention, of the above electronic camerafor generating a synthesized image having a wide dynamic range by usingflash emission in combination, the exposure condition designating meansincludes one or both of electronic shutter means for desirablycontrolling exposure amount by controlling photoelectric chargeaccumulation of the image pickup means and light shut off means forshutting off light from a light receiving surface of the image pickupmeans such that the control means controls one or both of the electronicshutter means and the light shut off means, and the flash emission meansto make an emission amount ratio by light from the flash emission meansas the same as an exposure amount ratio by normal light excluding thelight from the flash emission means at the two shots of picture taking.

By constructing in this manner, exposure amount ratios in the regionsdominated by exposure by normal light and in the regions dominated byexposure by flash emission of the flash emission means can be equalizedat the two shots of picture taking using flash emission, thereby asynthesized image is obtained as having an improved image quality.

In this aspect, the exposure amount ratio by normal light of the twoshots of picture taking is set by ratio of photoelectric chargeaccumulating time of the two shots at the image pickup means. Byconstructing in this manner, ratio of exposure amount by normal lightcan readily be set in the case where ratio of emission amount by normallight and ratio of emission amount by light from the flash emissionmeans are to be equally set between the two shots of picture taking.

In another aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, the flash emission means includessingle charge storage means for accumulating emission energy of theflash emission means such that the total of emission amounts at the twoshots of picture taking of the flash emission means is set equal to orlower than the total emission energy of the single charge storage means.It is thereby possible to effectively use charge of the single chargestorage means when light by the flash emission means is used at the twoshots of picture taking.

In still another aspect of the present invention, of the aboveelectronic camera for generating a synthesized image having a widedynamic range by using flash emission in combination, the flash emissionmeans includes a plurality of charge storage means differing from eachother in capacitance value for accumulating emission energy of the flashemission means such that a full emission of the flash emission means iscaused at each shot of the two shots of picture taking by selectivelyusing the plurality of charge storage means so as to make a differencein the total capacitance values to be respectively used. By thus causinga full emission of the flash emission means at the two shots of picturetaking, image pickup signals at an accurate emission amount ratio can beobtained without requiring an emission amount control (dimming control).

In yet another aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, the flash emission means includes aplurality of charge storage means for accumulating emission energy ofthe flash emission means such that one picture taking is performed by asmaller emission based on a full emission using one single or aplurality of charge storage means and the other picture taking isperformed by a larger emission based on an emission under dimmingcontrol using the other single or plurality of charge storage means. Byconstructing in this manner, the smaller emission can be caused to emitaccurately by a full emission without requiring dimming control and thelarger emission is caused to emit under dimming control so as to be ableto desirably set an emission amount ratio.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, the flash emission means includes aplurality of charge storage means for accumulating emission energy ofthe flash emission means such that one picture taking is performed by asmaller emission based on an emission under dimming control using onesingle or plurality of charge storage means and the other picture takingis performed by a larger emission based on a full emission using theother single or plurality of charge storage means. Thereby, the smalleremission is caused to emit under dimming control so as to be able todesirably set an emission amount ratio and the larger emission can becaused to emit accurately by a full emission without requiring dimmingcontrol.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, the flash emission means includesat least one charge storage means for accumulating emission energy ofthe flash emission means such that the two shots of picture taking areperformed as illuminated by a smaller emission and a larger emissioneach based on an emission under dimming control. By thus using anemission under dimming control for both of the two shots of picturetaking, due to the fact that full emission is not used, it is notnecessarily required to provide a separate individual emission means foreach and the value of emission amount ratio can be set more freely.

In this aspect, the dimming control may be effected by control ofemission time of the flash emission means. By thus effecting dimmingcontrol, a setting of emission amount can be accurately performedwithout requiring a photometry means.

Also, in this aspect, a photometry means may be provided such that thedimming control is effected based on detection of a predeterminedemission amount by direct photometry of the photometry means. In thecase where dimming control is effected in this manner, an actualemission amount can be measured so that control of light be effected toachieve a required emission amount in accordance with a reflectance ofthe object.

Furthermore, in this aspect, the dimming control may be effected basedon measurement and detection of a predetermined voltage at the chargestorage means. By constructing in this manner, dimming control can beeffected without using a photometry means and voltage measuring means atthe charge storage means for dimming control can be used in common withthe voltage measuring means of charging circuit of the charge storagemeans.

Moreover, in this aspect, when dimming is to be effected of the flashemission means at the second shot of picture taking, an emission amountof light from the flash emission means at the first shot of picturetaking is measured and an emission amount under dimming control of theflash emission means at the second shot is set based on the measuredemission amount so as to correspond to a previously set emission amountratio of the flash emission means between the two shots of picturetaking. By constructing in this manner, since variance in the firstemission amount of the flash emission means is actually measured andsuch variance can be corrected and absorbed at the setting of thecontrolled second emission amount, accuracy of the emission amount ratiocan be improved.

Further, in the case where, as in the above, variance in the firstemission amount is actually measured and such variance is corrected atthe setting of the controlled second emission amount, a photometry meansis provided so that the emission amount of the flash emission means atthe first shot of picture taking is measured by direct photometry of thephotometry means. By constructing in this manner, the first actualemission of the flash emission means can be measured so that a requiredemission amount in accordance with reflectance of the object be obtainedto accurately set the second emission amount.

Furthermore, in the case where, as in the above, variance in the firstemission amount is actually measured and such variance is corrected atthe setting of the controlled second emission amount, the emissionamount of the flash emission means at the first shot of picture takingis obtained by a voltage measurement at the charge storage means. Byconstructing in this manner, the first emission amount of the flashemission means can be measured without using a photometry means andvoltage measuring means at the charge storage means for the measurementof emission amount can be used in common with the voltage measuringmeans of charging circuit of the charge storage means.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, an emission amount of the flashemission means is measured to obtain an emission amount ratio based onsuch emission amounts and the exposure amount ratio by normal light isset as the same as such emission amount ratio. By constructing in thismanner, variance in the emission amount of the flash emission means canbe absorbed to obtain an accurate emission amount ratio and, by settingan exposure amount ratio equal to such emission amount ratio, asynthesized image can be obtained as having high image quality where theemission amount ratio and the exposure amount ratio are accuratelymatched.

In this aspect, an emission amount ratio may be obtained by measuring anemission amount of the flash emission means at a first shot of picturetaking and by computing a second emission amount by calculation based onthe first emission amount. Thereby, an emission amount ratio can beobtained only by the measurement of the first emission amount so that anexposure amount ratio be determined before the second emission.

Also, in this aspect, an emission amount ratio may be obtained bymeasuring emission amounts of the flash emission means at the first andsecond shots of picture taking. By constructing in this manner, a moreaccurate emission amount ratio can be obtained based on a result ofactual emissions.

Furthermore, in this aspect, a photometry means may be provided so as tomeasure an emission amount of the flash emission means based on directphotometry by the photometry means. By constructing in this manner, anactual emission by the flash emission means can be readily measured andan emission amount ratio can be accurately obtained by acquiring arequired emission amount in accordance with the reflectance of theobject.

Moreover, in this aspect, an emission amount of the flash emission meansmay be obtained by a voltage measurement at the charge storage means. Byconstructing in this manner, an emission amount of the flash emissionmeans can be measured without using a photometry means and voltagemeasuring means at the charge storage means for the measurement ofemission amount can be used in common with the voltage measuring meansof charging circuit of the charge storage means.

In accordance with the present invention, of the above electronic camerafor generating a synthesized image having a wide dynamic range by usingflash emission in combination, the flash emission means comprises onexenon emission tube and one charge storage means and is caused to emitat the two shots of picture taking by using the one xenon emission tubeand the one charge storage means. By constructing in this manner, theflash emission means can be constructed as having a small circuitrysize.

In accordance with the present invention, of the above electronic camerafor generating a synthesized image having a wide dynamic range by usingflash emission in combination, the flash emission means comprises onexenon emission tube, a plurality of charge storage means and chargestorage means switching means and is caused to emit at the two shots ofpicture taking by using the one xenon emission tube and at least one ofthe charge storage means switched and selected by the charge storagemeans switching means. In the case of such construction, since aplurality of units of charge storage means are provided, it is possibleto respectively control a smaller emission and a larger emission byusing charge storage means provided exclusively for each. Each emissioncan be performed independently so that an accurate emission control beeffected without reciprocally affected by each other.

In accordance with the present invention, of the above electronic camerafor generating a synthesized image having a wide dynamic range by usingflash emission in combination, the flash emission means comprises aplurality of xenon emission tubes, one charge storage means and xenonemission tube switching means and is caused to emit at the two shots ofpicture taking by using at least one xenon emission tube switched andselected by the xenon emission tube switching means and the one chargestorage means. By constructing in this manner, since a plurality ofunits of the xenon emission tube are provided, no reciprocal effectoccurs of consecutive emission at the two shots of picture taking and,therefore, the emissions can be effected respectively at a high accuracyirrespective of interval between emissions.

In accordance with the present invention, of the above electronic camerafor generating a synthesized image having a wide dynamic range by usingflash emission in combination, the flash emission means comprises aplurality of xenon emission tubes, a plurality of charge storage means,xenon emission tube switching means and charge storage means switchingmeans and is caused to emit at the two shots of picture taking by usingat least one xenon emission tube switched and selected by the xenonemission tube switching means and at least one charge storage meansswitched and selected by the charge storage means switching means. Byconstructing in this manner, since a plurality of units of chargestorage means are provided, it is possible to respectively control asmaller emission and a larger emission by using charge storage meansprovided exclusively for each and the emissions are not reciprocallyaffected because both can be performed independently. Also, since aplurality of units of the xenon emission tube are provided, noreciprocal effect occurs of two consecutive emissions and the emissionscan be effected respectively at a high accuracy irrespective of intervalbetween emissions.

In this aspect, the charge storage means may be constituted by one maincapacitor. By constructing in this manner, circuitry size can bereduced.

Also, in this aspect, the charge storage means may be constituted by aplurality of main capacitors connected in parallel. By constructing inthis manner, capacitance of a single main capacitor can be reduced sothat its production is easier. Also, for example, by making capacitanceof each main capacitor as the same as that of others to equalize ratioof the number of capacitors to be used in a smaller emission to thenumber of capacitors to be used in a larger emission and ratio of theiremission amounts (exposure amount ratio), a required emission amountratio can be controlled in an emission time of the same duration so thatcontrol is simpler.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, the respective emissions of theflash emission means at the two shots of picture taking are eacheffected as a single emission. By thus effecting the emissions at thetwo shots of picture taking respectively by a single emission, controlof emission is easier and variance in emission amounts can be reduced.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, the respective emissions of theflash emission means at the two shots of picture taking are effectedeither as one unit emission and a collection of a plurality of times ofunit emission or each as a collection of a plurality of times of unitemission. In such construction, since ratio of emitting unitscorresponds to a required, desirable emission amount ratio (exposureamount ratio) by setting an emission amount per unit emission to acertain fixed value, an advantage is achieved that the emission amountratio can be controlled by the number of emitting units. Also, emissionamount measuring means may additionally be provided to measure anemission amount of each unit emission of the collection of a pluralityof unit emissions so that an accurate emission amount ratio be obtainedby adjusting and controlling a total emission amount.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, the respective emissions of theflash emission means at the two shots of picture taking are effected asa smaller emission and a larger emission in that order. By thuseffecting the smaller emission first, control of the emission amount ofthe larger emission is easier, since the voltage drop at the maincapacitor of the charge storage means at start of the larger emission isrelatively small. As a result, accuracy in the emission amount ratio canbe improved. Also, in the case where the two emissions are consecutivelyeffected by the same flash emission means, some extent of reciprocaleffect occurs between the emissions. Since such effect produces a largereffect in the emission with a greater absolute value, the effect can bemitigated to an extent possible by effecting the smaller emission first.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, range finding means is providedsuch that an emission of the flash emission means is controlled to anoptimum emission amount corresponding to a distance information obtainedby the range finding means. By thus using a distance information, anemission amount can be set more accurately.

In this aspect, the emission to be controlled correspondingly to thedistance information is a smaller emission. While variance in emissionof the smaller emission is hard to be controlled by a real time emissioncontrol such as based on direct photometry of a photometric device orvoltage measurement at the charge storage means, it can be caused toemit relatively accurately by effecting a unitary emission by setting anabsolute value of emission amount based on a distance information.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, pre-photometry means is providedsuch that an emission of the flash emission means is controlled by usinga pre-photometry information obtained by the pre-photometry means. Bythus using a pre-photometry information where an actual luminance of theobject is measured, an absolute value of emission amount of a quantityof light corresponding to the luminance of the object can be obtained sothat an absolute value of emission amount can be set at a high accuracywithout using a distance information.

In a further aspect of the present invention, of the above electroniccamera for generating a synthesized image having a wide dynamic range byusing flash emission in combination, pre-photometry means is providedsuch that an emission of the flash emission means is controlled by usinga pre-photometry information obtained at the pre-photometry means bycausing a pre-emission of the flash emission means.

Since an emission amount is thus set based on a pre-photometryinformation which involves an additional actual emission of the flashemission means, a more precise absolute value of the emission amount canbe obtained.

In this aspect, the pre-photometry means may be formed by an externalphotometry means. By constructing in this manner, an absolute value ofemission amount of a quantity of light corresponding to the luminance ofan object can be obtained by using a photometry information of theactual object, and the external photometry means of the pre-photometrymeans can be used in common as the photometry means for emission of theflash emission means.

Also, in this aspect, the pre-photometry means may be used in common asthe image pickup means. By constructing in this manner, a separate,external photometry means is not required and an absolute value ofemission amount of a quantity of light corresponding to the luminance ofan object can be obtained by using a photometry information of theactual object.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of circuit of conventional synthesizing meansfor forming an image having a wide dynamic range by synthesizing twoimage pickup signals of different exposure amount.

FIG. 2 shows characteristics of weighting factors for input levels inthe synthesizing means shown in FIG. 1.

FIG. 3 is a block diagram of fundamental construction as a whole of anelectronic camera to which the present invention is applied.

FIG. 4 is a timing chart for explaining the conventional manner forgenerating two image pickup signals of different exposure amount usingan electronic shutter function and a means for shutting off light.

FIG. 5 is a timing chart for explaining the manner of generating twoimage pickup signals of different exposure amount in a first embodimentof electronic camera according to the present invention.

FIG. 6 illustrates the problems in the case of using a means forshutting off light in generating two image pickup signals of differentexposure amount.

FIG. 7 is a timing chart for explaining the manner of generating twoimage pickup signals of different exposure amount in a third embodimentof the present invention.

FIG. 8 is a schematic block diagram showing the construction of mainportion of a fourth embodiment of the present invention.

FIG. 9 is a timing chart for explaining the operation in the fourthembodiment shown in FIG. 8.

FIG. 10 is a timing chart for explaining the manner of generating twoimage pickup signals of different exposure amount in a fifth embodimentof the present invention.

FIG. 11 is a schematic block diagram showing the construction of mainportion of a sixth embodiment of the present invention.

FIG. 12 is a timing chart for explaining the operation of the sixthembodiment shown in FIG. 11.

FIGS. 13A and 13B illustrate the manner of a surplus emission of strobe.

FIG. 14 is a schematic block diagram showing the construction of mainportion of an eleventh embodiment of the present invention.

FIG. 15 is a schematic block diagram showing the construction of certainportions of a twelfth embodiment of the present invention.

FIG. 16 illustrates the problems in the case where a synthesized imagehaving a wide dynamic range is generated by synthesizing color imagesignals of different exposure amount using the conventional imagesynthesizing technique.

FIG. 17 illustrates the manner of occurrence of gradation when a strobelight is emitted against a wall surface.

FIGS. 18A and 18B show changes in level of image data with respect toposition and a manner of correcting gain thereof in the case where astrobe light is emitted by changing emission amount in the manner asshown in FIG. 17.

FIG. 19 illustrates the problems in the case where a synthesized imageis generated by synthesizing image data shown in FIGS. 18A and 18B.

FIG. 20 shows the manner of respective synthesized color signals of asynthesized color image in a thirteenth embodiment of the presentinvention.

FIG. 21 shows a color synthesized image signal in the case of synthesisof the thirteenth embodiment by emitting a strobe into a spacesurrounded by wall surfaces in the manner shown in FIG. 17.

FIG. 22 is a schematic block diagram showing the construction forachieving a synthesis by the thirteenth embodiment of the presentinvention.

FIG. 23 is a block diagram of circuit showing an example of constructionof the synthesizing circuit in FIG. 22.

FIG. 24 is a block diagram showing a fundamental construction of strobemechanism in the electronic camera shown in FIG. 3.

FIGS. 25A and 25B are each a block diagram showing an example ofconstruction of charge storage means in the strobe mechanism shown inFIG. 24.

FIG. 26 is a flowchart for explaining operation of a fourteenthembodiment of the present invention.

FIG. 27 is a block diagram showing an example of construction of strobemechanism to be used in a fifteenth embodiment of the present invention.

FIG. 28 is a block diagram showing an example of construction of strobemechanism to be used in a sixteenth embodiment of the present invention.

FIG. 29 is a block diagram showing another example of construction ofstrobe mechanism to be used in the sixteenth embodiment.

FIG. 30 is a block diagram showing a further example of construction ofstrobe mechanism to be used in the sixteenth embodiment.

FIG. 31 is a block diagram showing a further example of construction ofstrobe mechanism to be used in the sixteenth embodiment.

FIG. 32 is a block diagram showing a further example of construction ofstrobe mechanism to be used in the sixteenth embodiment.

FIG. 33 is a block diagram showing a further example of construction ofstrobe mechanism to be used in the sixteenth embodiment.

FIG. 34 is a block diagram showing an example of construction of thepart related to strobe mechanism to be used in a seventeenth embodimentof the present invention.

FIG. 35 is a flowchart for explaining operation of the seventeenthembodiment.

FIG. 36 is a block diagram showing an example of construction of thepart related to strobe mechanism to be used in an eighteenth embodimentof the present invention.

FIG. 37 is a block diagram showing an example of construction of thepart related to strobe mechanism to be used in a nineteenth embodimentof the present invention.

FIG. 38 is a flowchart for explaining operation of the nineteenthembodiment.

FIG. 39 is a block diagram showing an example of construction of thepart related to strobe mechanism to be used in an twentieth embodimentof the present invention.

FIG. 40 is a flowchart for explaining operation of the twentiethembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the present invention will now be described. First,a description will be given below by way of a block diagram shown inFIG. 3 with respect to a fundamental construction as a whole of anelectronic camera to which the present invention is applied. Referringto FIG. 3, denoted by numeral 1 is a single-plate color CCD image pickupdevice for photoelectrically converting an optical signal into anelectrical signal. It includes an electronic shutter function. Lightfrom an object is inputted to the CCD image pickup device 1 through lens2 and stop/shutter mechanism 3. The output of CCD image pickup device 1is amplified at an amplifier 4 after removed of noise for example at acorrelation double sampling circuit. An analog-to-digital converter 5converts the output of the amplifier 4 outputted as analog data intodigital data. A camera signal processing circuit 6 processes signalsfrom the CCD image pickup device 1 as a video data. What is denoted bynumeral 7 including AF detector circuit for extracting AF information tocontrol focus, AE detector circuit for extracting AE information tocontrol exposure and AWB detector circuit for extracting AWB informationto set white balance, uses image pickup signals, etc., from CCD imagepickup device 1 prior to the primary picture taking. The output signalsfrom the AF, AE and AWB detector circuits 7 provide through CPU 8 an AFinformation to lens 2, an AE information to stop/shutter mechanism 3 andan AWB information to the camera signal processing circuit 6.

Numeral 9 denotes a compression circuit (JPEG) for compressing theamount of data. The image data compressed at the compression circuit 9is recorded at memory card 15 through memory card I/F 14. Memorycontroller 10 and DRAM 11 are used as working memory when performingcolor processing, etc., of video data. A display circuit 12 and LCDdisplay unit 13 are used for example to confirm the picture takingconditions by reading out and displaying data recorded at the memorycard 15. Denoted by numeral 16 is a personal computer I/F fortransferring data recorded on the memory card 15 to a personal computer17. It should be noted that, in FIG. 3, numeral 18 denotes a timinggenerator which generates timing pulse for driving the CCD image pickupdevice 1. It drives the CCD image pickup device 1 according to controlof CPU 8. Numeral 19 denotes a strobe mechanism which is controlled byAE information through CPU 8. Numeral 20 denotes input keys of the CPUby which setting of various types of picture taking mode, driving oftrigger switch, etc., can be performed.

Operation of an electronic camera having the above construction issummarized as follows. Image pickup signals generated by means of twotimes of picture taking under different exposure conditions by using theCCD image pickup device 1 are respectively converted into digital signalat the analog-to-digital converter 5. After subjected to predeterminedsignal processing at the camera signal processing circuit 6, they aretemporarily stored as image data to DRAM 11. In accordance with controlby CPU 8, of the above two image data, image data for high luminanceregions of the object are then selected from the image data of smallerexposure amount and image data for low luminance regions of the objectare selected from the image data of larger exposure amount. Byperforming a predetermined synthetic operation processing using theselected two image data, it is possible to obtain a single synthesizedimage data which has a wide dynamic range as a whole. The synthesizedimage data is subjected to compression at the compression circuit 9 andis recorded at the memory card 15.

A description will now be given with respect to a first embodimentaccording to the present invention of technique for obtaining anincreased wide dynamic range by reading out and synthesizing two imagepickup signals of different exposure amount in an electronic camerawhich is constructed as the above. In the above described conventionalexample as disclosed in Japanese patent application laid openNo.4-207581, as shown in FIG. 4, an electronic shutter function of CCDimage pickup device is used to perform a first shot of picture taking toobtain image pickup signal of smaller exposure amount and means forshutting off light (shutter) is used to perform a second shot of picturetaking to obtain image pickup signal of larger exposure amount. Includedin FIG. 4 are: first shot, {circle around (1)}: second shot, {circlearound (2)}; vertical synchronizing signal, VD; and charge accumulatingtime for the second shot, T₂.

In the first embodiment of the present invention, as shown in FIG. 5, afirst shot {circle around (1)} for obtaining image pickup signal ofsmaller exposure amount is performed by using an electronic shutterfunction of CCD image pickup device in a similar manner as theconventional example. On the other hand, when a charge accumulating timeT₂ (time to be set in accordance with the conditions of the object) ofCCD image pickup device for a second shot {circle around (2)} to obtainimage pickup signal of larger exposure amount is set as longer than timeT₀ (usually equals to the period of one vertical synchronizing signal)required for readout of all the pixels of CCD image pickup device, theimage pickup signal of larger exposure amount is generated by using theelectronic shutter function of CCD image pickup device.

In particular, since readout of the image pickup signal of smallerexposure amount is complete at the end of the charge accumulating timeof CCD image pickup device for obtaining image pickup signal of largerexposure amount, the electronic shutter function can be used in settingof a charge accumulating time for obtaining image pickup signal oflarger exposure amount. By using the electronic shutter function in thismanner, it is possible to control the charge accumulating time moreaccurately than in the case of using means for shutting off light. Itshould be noted that all the operations of the above described CCD imagepickup device, means for shutting off light, etc., are controlled bycontrol signals from CPU.

A second embodiment will now be described. Usually in the case wheremeans for shutting off light is included in an electronic camera, it isused while the means for shutting off light is kept opened. If a pictureis to be taken by setting a charge accumulating time, the chargeaccumulating time is set by closing the means for shutting off light. Astart of charge accumulating time is effected by applying a shutterpulse to the CCD image pickup device in a similar manner as anelectronic shutter so as to discharge unwanted charge to startphotoelectric conversion. Accordingly, if a focal-plane shutter is usedas the means for shutting off light, only the second blind is operatedto set the charge accumulating time. As shown in FIG. 6, a difference incharge accumulating time due to the moving of the second blind occursfrom one pixel to another on a light receiving surface 21 of CCD imagepickup device depending on their positions (for example between theleading edge and trailing edge). As a result, an occurrence of shading22 having a constant inclination cannot be avoided in the image pickupsignals. It should be noted that, in FIG. 6, shutter position A, Brespectively represents a position of the leading edge of the secondblind.

In the present embodiment, in order to eliminate this, the shading iscorrected by providing a shading correction means having acharacteristic reciprocal to the above described inclination. Thisshading correction means is provided for example in a camera signalprocessing circuit to perform shading correction by means of signalprocessing.

A third embodiment will now be described. This embodiment is adapted tobe capable of preventing an occurrence of shading when a focal-planeshutter is used as the means for shutting off light in setting a chargeaccumulating time. In particular, as shown in FIG. 7, an electronicshutter function of CCD image pickup device is used first to perform afirst shot {circle around (1)} of smaller exposure amount, so as togenerate a first image pickup signal. Then, the charge accumulatingoperation to the CCD image pickup device is temporarily haltedimmediately after the completion of the above electronic shutteroperation. This is performed for example by continuing a dischargingoperation of unwanted charge. In this charge accumulation halting periodt₁, a shutter charge of the focal-plane shutter is performed in order toachieve a state where both the first blind and second blind of thefocal-plane shutter can be used. After the completion of the shuttercharge, the charge accumulating operation of CCD image pickup device isstarted. A normal focal-plane shutter operation is then performed wherethe both blinds of the focal-plane shutter are operated, therebyperforming a second shot of picture taking {circle around (2)} witheffecting control of exposure time (actual charge accumulating time) t₂,so as to generate a second image pickup signal. Since the second imagepickup signal is obtained from a normal focal-plane shutter operation,no shading occurs and, therefore, shading correction means becomesunnecessary. It should be noted that, in FIG. 7, A, B respectivelyrepresents a position of the shutter (positions corresponding to A, B inFIG. 6).

A fourth embodiment will now be described. In this embodiment, as shownin FIG. 8, a photometric device 31 having a separated entity from CCDimage pickup device 1 is disposed near the CCD image pickup device 1.The charge accumulating time of CCD image pickup device 1 in a secondshot is set in such a manner as to correspond to a predetermined ratioof exposure amount between two shots of picture taking, based on anexposure amount actually measured at the above photometric device 31 atthe time of the first shot.

In particular, the exposure amount ratio of the two shots are previouslydetermined for example as 1:8 or 1:16. A first shot {circle around (1)}is thus performed as shown in FIG. 9 by setting a charge accumulatingtime in such a manner as to result an exposure amount of ⅛ or {fraction(1/16)} of AE value obtained before the picture taking. A first imagepickup signal is thereby generated. At this time, actual exposure amountis measured by the photometric device 31. Then, based on the actuallymeasured exposure amount, the charge accumulating time of CCD imagepickup device at the time of second shot is set in such a manner as tocorrespond to the predetermined exposure amount ratio (for example 1:8or 1:16) of the two shots of picture taking, and the second shot {circlearound (2)} is performed to generate a second image pickup signal. Thetwo image pickup signals are then synthesized to form an image having awide dynamic range. In this case, since the charge accumulating time inthe second shot {circle around (2)} is based on the actual exposureamount measured by a photometric device, an accurate control of theactual exposure amount ratio is possible between the two image pickupsignals.

A fifth embodiment will now be described. In this embodiment, a strobeemission timing in the case of picture taking using a strobe incombination is suitably controlled so that an occurrence of false colorin the synthesized image can be prevented to an extent possible. Inparticular, as shown in FIG. 10, a strobe is caused to emit at one orboth of timing at t₃ in the second half of the charge accumulating timein the first shot {circle around (1)} or timing at t₄ in the first halfof the charge accumulating time of the second shot {circle around (2)}.

Thereby, although an occurrence of time difference between the two shotsof picture taking is unavoidable, it is controlled to a minimum and anoccurrence of false color in the synthesized image is reduced to anextent possible. In addition, by reducing the time difference, theinfluence of shaking can also be mitigated.

A sixth embodiment will now be described. In this embodiment, too, astrobe emission is used to generate two image pickup signals ofdifferent exposure amount. However, since actual emission amount of astrobe varies, an emission amount ratio is actually measured by using aphotometric device so that an exposure amount ratio is setcorrespondingly to such emission amount ratio.

In particular, as shown in FIG. 11, a photometric device 31 is disposednear the CCD image pickup device 1 and an emission is effected in bothof the two shots of picture taking by a strobe mechanism 19. These twostrobe emission amounts are set to a predetermined exposure amountratio, for example, 1:8 or 1:16. As shown in FIG. 12, an emission iseffected at a timing in the second half of the first shot and at atiming in the first half of the second shot. Since, however, a varianceoccurs in the actual strobe emission, the ratio of the strobe emissionamounts is measured by the above described photometric device 31 and thecharge accumulating time at the second shot of picture taking is set insuch a manner as to correspond to the actually measured emission amountratio. In the case where two image pickup signals of different exposureamount are generated by using a strobe emission, too, an accuratecontrol of the exposure amount ratio can be achieved correspondingly tothe strobe emission amount ratio even with a variance occurring instrobe emission. It should be noted that, in this case, synthesis of thetwo image pickup signals is performed based on the exposure amount ratiocorresponding to the actually measured emission amount ratio.

A seventh embodiment will now be described. Generally, a strobe emissionaccompanies a surplus emission. In particular, as shown in FIG. 13A, astrobe emission accompanies a surplus emission even after the stoppingof the emission, resulting in a mountain like curve. When represented inintegrated values, this results in a curve leading to a saturation asshown in FIG. 13B. An error in emission amount due to such surplusemission is larger in its proportion as the emission amount is smaller.Thus, in the present embodiment, at the first smaller emission of thetwo emissions, an emission stop timing (timing of an emission stopsignal) and completion timing of the electronic shutter operation of CCDimage pickup device are brought to the same point in time so that aninfluence of such surplus emission be eliminated in setting an exposureamount ratio.

An eighth embodiment will now be described. In this embodiment, whengenerating two image pickup signals of different exposure amount, adiaphragm stop value of lens at the two shots of picture taking isfixed, thereby the image pickup signals are obtained as having an equaldepth of field. It is thereby possible to prevent a false colorresulting from a synthesis of an image in focus and an image out offocus.

The diaphragm stop value to be used here is the diaphragm stop value atan optimum diaphragm stop value and shutter speed obtained by theexposure setting means prior to the picture taking. Then, the aboveoptimum diaphragm stop value and shutter speed are used at a shot fortaking image pickup signal of larger exposure amount. At the time ofshot for taking image pickup signal of smaller exposure amount, the samediaphragm stop value as the above is used while the shutter speed is setin accordance with a predetermined exposure amount ratio.

Further, photometry in obtaining the optimum diaphragm stop value andshutter speed at the exposure setting means may be performed either byusing CCD image pickup device, or by using an external photometricdevice provided separately from the CCD image pickup device.

A ninth embodiment will now be described. In this embodiment, when twoimage pickup signals of different exposure amount are generated andsynthesized, there is provided means for performing a white balancecorrection by using the same white balance correction value with respectto the two image pickup signals before such synthesis. Thereby, anoccurrence of false color in the synthesized image is prevented.

Here, the correction value to be used in the above white balancecorrection is the white balance correction value obtained by whitebalance setting means before the picture taking, and the white balancecorrection is performed on the two image pickup signals before thesynthesis. It is also possible to set a white balance correction valuebased on the two actually obtained image pickup signals.

Further, in general, it is necessary that a white balance be set for theportion of the main object of an image. The portion to become the mainobject of an image is more likely to be included in the image pickupsignal of larger exposure amount. Accordingly, a white balancecorrection value can be efficiently determined and the synthesis can beperformed with an optimized white balance of the main object byobtaining a white balance correction value based on the larger-exposureimage pickup signal of the two image pickup signals.

A tenth embodiment will now be described. In this embodiment, instead ofperforming white balance correction respectively for the two imagepickup signals of different exposure amount before synthesis, whitebalance correction means is constructed to perform white balancecorrection with respect to an image after the synthesis. It is therebypossible to efficiently perform a white balance correction. The whitebalance correction value to be used in this case, too, may either be awhite balance correction value obtained by white balance setting meansbefore the picture taking or be one obtained based on an alreadysynthesized image. It can also be one set based on the two image pickupsignals before performing the synthesis. Also, in this case, the whitebalance correction value can be set based on the image pickup signal oflarger exposure amount of the two image pickup signals before performingthe synthesis.

An eleventh embodiment will now be described. Normally, two image pickupsignals of different exposure amount are fixed of gain when subjected tosynthesis. In an electronic camera performing such synthesis, generationof two image pickup signals by taking picture at an exposure amountratio of 1:8, for example, requires a shutter speed ratio of ¼:{fraction(1/32)}. A shutter mechanism, however, is normally provided with theshutter speeds of ¼, ⅛, {fraction (1/15)}, {fraction (1/30)}, {fraction(1/60)}, {fraction (1/125)}, {fraction (1/250)}, {fraction (1/500)},etc. Image pickup signals at an accurate exposure amount ratio cannot begenerated, if an attempt for correspondence is made by using shutterspeeds of ¼:{fraction (1/30)}.

In the present embodiment, thus, gain control means 35 is provided asshown in FIG. 14 at a stage succeeding the amplifier 4 so that differentgain values can be respectively set for the two image pickup signals ofdifferent exposure amount. Here, in this aspect, the gain values for twoimage pickup signals are set so that the exposure amount ratio of twoimage pickup signals corresponds to a predetermined exposure amountratio (image synthesizing ratio). Even when shutter speed cannot beaccurately adapted to an exposure amount ratio, an image pickup signalequivalent to the case of picture taking at a shutter speed of {fraction(1/32)}, for example in the above exemplary case, can be obtained bychanging the gain value of image pickup signal taken at the shutterspeed of {fraction (1/30)}. It is thereby possible to generate two imagepickup signals which are accurately set to an exposure amount ratio.

A twelfth embodiment will now be described. In this embodiment, when twoimage pickup signals of different exposure amount are generated, thediaphragm stop value of lens is changed while fixing the chargeaccumulating time to generate the image pickup signals of differentexposure amount. Image pickup signals at a predetermined exposure ratiocan thus be obtained without precisely controlling the chargeaccumulating time.

In this aspect, degree of peripheral attenuation (phenomenon of loweredilluminance in proportion to the fourth power of cosine of angle ofview) is changed due to the change in diaphragm stop value of lens. Toremove such peripheral attenuation, a peripheral attenuation correctioncircuit 42 is provided as shown in FIG. 15 to correct the peripheralattenuation in accordance with the diaphragm control by a diaphragmcontrol circuit 41. It is thereby possible to correct the peripheralattenuation occurring due to a change in the diaphragm stop value oflens.

Further, as shown in FIG. 15, in the case where a strobe emission isused to generate two image pickup signals of different exposure amount,two emissions equal to each other in emission amount are effected andthe diaphragm stop value of lens is changed so as to generate imagepickup signals of different exposure amount. The emission amount ratioof strobes and the exposure amount ratio of ambient light can thus bemade equal to each other without requiring a precise control of strobe'semission amount.

A thirteenth embodiment will now be described. This embodiment relatesto image synthesizing technique in forming a synthesized image having awide dynamic range by synthesizing two image pickup signals of differentexposure amount.

As has been described above, in fundamental of the image synthesizingtechnique disclosed in Japanese patent application laid openNo.6-141229, a saturated portion in the image pickup signal of largerexposure amount is replaced by the image pickup signal of smallerexposure amount. In such replacing operation, a gain correctionaccording to exposure amount ratio is performed to obtain a synthesizedimage which is linear and possesses a wide dynamic range. An inclinedweighting factor is assigned at the time of the synthesis to effect asmooth switching in an overlapping manner.

However, if this technique is simply applied to color image signals,there occurs a problem as follows. In particular, supposing R, G signalsdiffering in output level with respect to luminance as shown in FIG. 16,synthesized by weighting factors such as of the above with a determinedlevel of 100%, it is in actuality often impossible to obtain a linearsynthesizing output due to variance in device, even when the synthesisis performed in accordance with an exposure amount ratio. It should benoted that, in FIG. 16, solid lines represent the synthesizing imagedata of G, R signals, the illustrated case indicating that actual levelof the image data of smaller exposure amount is lower than that by theexposure amount ratio. In such case, since ratio between G signal and Rsignal is changed in the range α where the linear characteristic is notpreserved, the color is not correctly reproduced and appears as a falsecolor. In the disclosure in the above publication, this point is nottaken into consideration at all.

By contrast, Japanese patent application laid open No.7-131708 disclosesa synthesizing technique in which one obtained from actual image data isused as the synthesizing ratio in actual synthesis between image pickupsignal of larger exposure amount and image pickup signal of smallerexposure amount. By applying this synthesizing technique, the problem inthe technique disclosed in the above Japanese patent application laidopen No.6-141229 is fundamentally eliminated.

However, if strobe emission is applied to the synthesizing techniquedisclosed in Japanese patent application laid open No.7-131708, thereoccurs a problem as follows. In particular, a mode is supposed here asthe scene of picture taking using a strobe emission that, when there isa wall on the left side within a room as shown in FIG. 17, a strobe isemitted against the wall, whereby a gradation of luminance occurs suchthat the near side is brighter and it gets darker toward the far sidewith respect to the strobe light. In this mode, a fixed level of ambientlight is assumed. When picture is taken by a longer exposure time(larger exposure amount) with emitting a strobe, the manner of level ofimage data with respect to positions is represented as diagrammaticallyin FIG. 18A. On the other hand, when picture is taken by a shorterexposure time (smaller exposure amount) by changing exposure amount andstrobe emission amount (for example 1:4), an image data results asindicated by the dotted line in FIG. 18B. The solid line represents whatis derived from gain correction (for example 4 times) of such imagedata.

The ambient light level thus corrected of gain results in the same levelof ambient light as in the longer exposure time shown in FIG. 18A. Inactuality, however, it is hard to make a strobe light emit at anaccurate ratio (for example 1:4) and a variance results. The exampleshown in this figure is of the case where the strobe emission amount inthe shorter exposure time is beyond what is suitable. When image pickupsignal of longer exposure time and image pickup signal of shorterexposure time such as shown in FIGS. 18A and 18B are synthesized, theportion depending on the ambient light alone is correctly synthesized asshown in FIG. 19. However, in the portion where a gradation occurs ofthe strobe light, an abrupt difference in luminance as shown results inthe synthesized image due to the variance in the emission amount ratio.A pseudo contour occurs at the portion of such abrupt difference,resulting in a problem that even the case of smoothly changing luminancesuch as a wall is synthesized as if there is a contour.

The present embodiment is thus made to eliminate such problem. When asaturation of color signal occurs in one of R, G, B, color signals inthe image pickup signal of longer exposure time (larger exposureamount), i.e., when it is to be replaced by signal of shorter exposuretime (smaller exposure amount), a similar substitution is performed atthe same time with respect to all the color signals. In performing suchsubstitution, the color signals are added with assigning the sameweighting factor to all of them to effect the substitution.

In particular, as shown in FIG. 20, if G signal of longer exposure timefor example reaches its saturation level of 100%, it is replaced by asignal of shorter exposure time which is corrected of gain by theweighted addition. At the same time, R signal, too, is switched tosignal of shorter exposure time which is corrected of gain by using thesame weighting factor. In this aspect, since such switching is performedby using the same weighting factor for all the color signals even thoughthere may be a small error, the problem of occurrence of a false colorat the point of such switching is eliminated. Synthesis is then smoothlyeffected by changing the weighting factor in such a manner as to have anoverlap at the portion of switching similarly to the weighting factor(see FIG. 2) disclosed in the previously demonstrated Japanese patentapplication laid open No.6-141229, so as to replace the signal of longerexposure time by the signal of shorter exposure time. The change inluminance thus occurs gradually even in the synthesized signal as shownin FIG. 21, and an occurrence of pseudo contour can be prevented evenwhen a strobe emission is used.

As a synthesizing circuit to be actually used here, one suffices to havethe construction as shown in FIG. 22 in which image pickup signals fromCCD image pickup device 1 are subjected to analog-to-digital conversionat an A/D converter 5, synthesizing process at a synthesizing circuit 51and compression at a compression circuit 52, so as to effect anoperation corresponding to the dynamic range of an output system. Here,for example as shown in FIG. 23, the synthesizing circuit comprises: amaximum output detection circuit 61 for outputting the highest(luminance) one out of color signals R_(L), G_(L), B_(L), in color imagepickup signal of the longer exposure time; a weighting factor generationcircuit 62 for generating weighting factor correspondingly to theluminance of the color signal possessing the highest value outputtedthrough the maximum value detection circuit 61; multipliers 63 and 64for respectively multiplying color signals R_(L), G_(L), B_(L), of thecolor image pickup signal of the longe r exposure time and color signalsR_(S), G_(S), B_(S), of the color image pickup signal of the shorterexposure time respectively by the same weighting factors set at theweighting factor generation circuit 62; and an adder 65 for adding, withrespect to each color signal, the respective color signals multiplied bythe weighting factors. It should be noted that color signals R_(S),G_(S), B_(S) are the signals corrected of gain with respect to thedifference in signal level due to the difference in charge accumulatingtime, by a factor obtained from the ratio of charge accumulating time orfrom actual image data.

In the synthesizing circuit constructed as the above, one having thehighest value among the color signals. R_(L), G_(L), B_(L), of colorimage pickup signal of longer exposure time is detected at and outputtedfrom the maximum value detection circuit 61. In accordance with theluminance value of thus detected and outputted color signal having thehighest value, weighting factors for the respective color signals oflonger exposure time and shorter exposure time are generated at theweighting factor generation circuit 62. Color signals R_(L), G_(L),B_(L), of image pickup signal of the longer exposure time and colorsignals R_(S), G_(S), B_(S), of image pickup signal of shorter exposuretime are respectively multiplied by the same weighting factors at themultipliers 63 and 64. Then, each weighted color signal is respectivelyadded at the adder 65 to generate R, G, B synthesized signals having awide dynamic range. While this embodiment has been described by usingRGB signal as the color signal, its scope is not limited to this and itmay also be applied in a similar manner to other color signals such asof a complementary color system.

Embodiments have been described herein of the case where a syntheticimage having a wide dynamic range is formed by taking picture by jointlyusing a strobe light in the above fifth embodiment (see FIG. 10), sixthembodiment (see FIGS. 11 and 12), seventh embodiment (see FIGS. 13A and13B), twelfth embodiment (see FIG. 15), and thirteenth embodiment (seeFIGS. 20 to 23). A detailed description will now be given collectivelywith respect to such case where a synthesized image is generated bytaking picture by jointly using a strobe light, and some otherembodiments related thereto will also be described below.

First, a description will be given by way of FIG. 24 with respect to afundamental construction of the strobe mechanism 19 in the block diagramof an entire electronic camera shown in FIG. 3. FIG. 24 includes: axenon emission tube 71; an emission control circuit 72 for supplyingemission energy to the xenon emission tube 71; and charge storage means73 for accumulating the emission energy of the xenon emission tube. Thecharge storage means 73 is charged from a power supply 75 through acharging circuit 74. Such charging of the charge storage means 73through the charging circuit 74 is controlled by a control signal fromCPU 8 which monitors the charging voltage of a main capacitor of thecharge storage means 73 in order to control the charging voltage to aconstant voltage so that a charging operation is complete upon anattainment of the constant voltage. On the other hand, operations tostart an emission and stop an emission of the xenon emission tube 71 areperformed by outputting control signal to the emission control circuit72 through CPU 8 by means of operation of an external input key.

Not only one constructed as having a single main capacitor 73-1 as shownin FIG. 25A but also one constructed as connecting in parallel aplurality of main capacitors 73-1 a, 73-1 b, 73-1 c, 73-1 d, etc., asshown in FIG. 25B can be used as the above charge storage means 73. Itshould noted that capacitance of each of the main capacitors may eitherbe the same as that of another or be different from that of another.Those constructed as shown in FIGS. 25A, 25B are selectively used,unless otherwise specified, as the charge storage means in theembodiments to be described in the following.

A basic embodiment of the case of using a strobe light in combination isdefined as a fourteenth embodiment and its operation will be describedbelow by way of a flowchart shown in FIG. 26. In this embodiment, abasic strobe mechanism as shown in FIG. 24 is used. First, emissionamount is set of two emissions in the two shots of picture taking by oneunit of the charge storage means (step 101), so as to effect an emissionrespectively at the two shots of picture taking. In this aspect, it ispossible either to accurately set the emission amount in numerical valuefor both of the two emissions so as to bring their total within anemission amount corresponding to the one unit of charge storage means,or to simply provide a constraint so that the total of two emissionamounts fall into the range corresponding to the capacitance value ofthe one unit of charge storage means. After such setting, a strobeemission in a first shot (step 102) and a strobe emission in a secondshot (step 103) are effected to generate two image pickup signals.

It should be noted that the setting of two emission amounts in the abovetwo shots of picture taking can also be set such that two emissionamounts of xenon tube are set by using AE information outputted throughan AE detector circuit by means of image pickup signal obtained from CCDimage pickup device before the actual taking of picture, i.e.,pre-photometry information. By thus using the pre-photometry informationcorresponding to the brightness of the object to be actuallyphotographed, it is possible to set an emission amount to a quantity oflight corresponding to the brightness of the object. Further, it is alsopossible to provide an external photometric device to use an integralinformation from the external photometric device instead of image pickupsignal as AE information (pre-photometry information) for performingcontrol as to whether or not to effect a strobe emission and control onthe quantity of light of the strobe emission. It is furthermore possibleto cause a pre-emission at the strobe mechanism 19 before the primarypicture taking so as to take an information of the object obtained atthat time from the CCD image pickup device or external photometricdevice as a pre-photometry information. Setting of the emission amountcan also be performed by using this pre-photometry information. Since,thereby, setting of the emission amount can be performed based on thepre-photometry information which accompanies an actual emission of thestrobe mechanism, an emission amount can be set at a higher accuracy.

By causing two emissions by setting emission amount in this manner, anaccumulated charge of one charge storage means is effectively used inthe two shots of picture taking so as to cause the two emissions.Effecting of the above two emissions is either of the case where therespective amounts of the two emissions are made equal to each other bysetting an emission amount ratio of 1:1, or of the case where therespective amounts of the two emissions are set differently from eachother by setting an emission amount ratio of 1:N (N being an optionalreal number). In the case where the emission amount ratio is set to 1:N,the first and/or second emission may be divided into a plurality oftimes of emission so as to obtain the emission amount ratio of 1:N. Ifeach emission is performed as a collection of a plurality of times ofunit emission, any required emission amount ratio is achieved by theratio of number of unit emissions by determining a constant emissionamount for each unit emission. Control of the emission amount ratiobecomes easier.

Also, an accurate emission amount ratio can be obtained by additionallyproviding emission amount measuring means to measure the emission amountat each unit emission in the collection of a plurality of unit emissionsso as to adjust and control a total emission amount.

Similarly, of main capacitors of electric charge storage means, if theratio between the numbers of main capacitors to be used respectively inthe first time and in the second time is made equal to the emissionamount ratio (exposure amount ratio) by setting the capacity of eachcapacitor to the same value, control becomes simpler because a requiredemission amount ratio can be controlled in the same emission time. Whilea description has been made in the above by regarding a main capacitoras one unit, a similar advantage can be achieved by treating as oneunit, instead of a main capacitor, a charge storage means which is acollection of a number of main capacitors.

Now, when two shots of picture taking are performed by changing theemission amount of strobe emission, a difference in the exposure amountratio of the taken images obtained by the two shots of picture takingoccurs between the portion without receiving any strobe light, i.e.,exposed only by normal light, and the portion impinged upon and exposedby strobe light, within the photographed image obtained by the picturetaking using strobe emission. This results in a problem of degradedimage quality of the synthesized image.

A fifteenth embodiment to be described below is thus made to eliminatethis problem. In the fifteenth embodiment, the exposure amount ratio ofthe two shots of the portion taken only by normal light is made equal tothe emission amount ratio of the strobe light of the two shots.

In particular, an exposure amount ratio of the two shots of picturetaking in the region not reached by strobe light and dominated byexposure by normal light is made as the same as the emission amountratio (exposure amount ratio) of the two shots of picture taking in theregion where exposure by strobe light is dominant. It is therebypossible to obtain a synthesized image of an improved image quality.

In performing two shots of picture taking by setting the exposure amountratio of normal light as the same as the emission amount ratio of strobelight, the ratio of amount of exposure by normal light between the twoshots is set by ratio between the two shots of photoelectric chargeaccumulating time of the image pickup device. The ratio of exposureamount by normal light can thus be readily set.

On the other hand, the emission amount ratio of strobe light between thetwo shots is set by changing time duration of emission of strobe light.In particular, since relation between emission amount of strobe and itsemission time duration is experimentally known in advance, a tableindicating such relation can be internally provided so that it be usedto readily set the emission amount ratio by setting emission time. It isalso possible to set an emission amount ratio such that an actualemission amount or voltage value of charge storage means is measured andan emission is controlled in such a manner as to achieve a predeterminedemission amount ratio.

Further, in the case where an emission amount ratio of strobe light isset in a manner as the above by changing emission time or by determiningan emission amount or voltage value of charge storage means to beactually measured, it is so set that a picture is taken by using asmaller emission at the first shot and a larger emission at the secondshot. In other words, by effecting exposure of short time duration firstand then exposure of long time duration, each emission can be startedfrom the state where the charging voltage of main capacitor of thecharge storage means is high. Its control is thus easier and an emissionamount ratio can be controlled at a relatively high accuracy. Bycontrast, if a larger emission is used at the first shot, a greaterdifference in charging voltage value of main capacitor of the chargestorage means occurs between the two emissions, making it harder tocontrol the emission amount ratio.

Further, while the two times of emission, the smaller emission andlarger emission, can be effected by using a single xenon emission tubeand a single charge storage means as in the fundamental constructionshown in FIG. 24, it is also possible to employ a construction where, asshown in FIG. 27, xenon emission tubes 71 a and 71 b are providedexclusively for a larger emission and a smaller emission, respectively.The emissions are caused with respect to a single charge storage means73 by way of a xenon emission tube switching means 80 and respectiveemission control circuits 72 a and 72 b. In the case where twoconsecutive emissions are caused by using a single xenon emission tube,since a reciprocal effect may occur in the two emissions, it isnecessary to have some measures such as provision of a requisite for anincreased interval between the two emissions. However, by using theexclusive xenon emission tubes as in the above, the reciprocal effectbetween two consecutive emissions is completely eliminated and each canbe caused to emit respectively at a highly accurate emission amount. Itshould be noted that the number of xenon tubes is not limited to two andit is also possible to provide three or more units so that one or aplurality of xenon emission tubes are selectively used therefrom.

In the above fourteenth and fifteenth embodiments, a portion of chargesof a single unit of charge storage means is used respectively in eachemission of the two flash emissions so that each emission corresponds toa predetermined emission amount ratio. However, for example, a xenonemission tube is limited in its voltage range where an emission can bestarted. In order to perform the two emissions by the same chargestorage means, it is necessary to provide a restraint on the firstemission amount so that the voltage of main capacitor of the chargestorage means at start of the second emission is maintained above avoltage capable of causing an emission of the xenon emission tube.Further, a strobe emission can be controlled accurately by a simpleconstruction as a full-emission where all the charge accumulated at amain capacitor is totally used by a single emitting operation.

In a sixteenth embodiment, therefore, the above described smalleremission and larger emission are each caused by using one or a pluralityof exclusive charge storage means. By thus using an exclusive chargestorage means for each emission, the above described restraint is notrequired. Further, by having exclusive charge storage means, at leastone emission at the two shots of picture taking can be caused as afull-emission so that accuracy thereof is improved. In particular, inaddition to taking of picture by controlling both of the two emissions(smaller emission and larger emission) by control (dimming) of theemission amount such as by controlling emission time, it is alsopossible to perform picture taking where one of the emissions (smalleremission or larger emission) is performed as a full-emission and theother emission (larger emission or smaller emission) is controlled withrespect to emission amount such as by controlling emission time.Furthermore, it is possible that both emissions are performed asfull-emission so as to take a picture at a highly accurate emissionamount ratio.

In the case where an exclusive charge storage means is thus used foreach emission, it is possible to employ either a construction where, asshown in FIG. 28, two xenon emission tubes 71 a, 71 b are provided andare respectively combined with separate charge storage means 73 a, 73 bthrough emission control circuits 72 a, 72 b to meet the smalleremission and larger emission, or a construction where, as shown in FIG.29, two charge storage means 73 a, 73 b are used for one xenon emissiontube 71 by switching them through a changeover switch 76. If a singlexenon emission tube is thus used in common, it is possible to achieve areduction in circuitry size.

While FIGS. 28 and 29 show a combination of two xenon emission tubes andtwo charge storage means through emission control circuits, or acombination of one xenon emission tube and two charge storage meansthrough an emission control circuit and a changeover switch, it is alsopossible that the smaller emission and larger emission are respectivelyperformed by combining optional xenon emission tubes and optional chargestorage means. For example, as shown in FIG. 30, it is also possible touse a construction where only certain ones out of a plurality of chargestorage means can be connected to one xenon emission tube. Inparticular, two xenon emission tubes 71 a, 71 b and four charge storagemeans 73 a, 73 b, 73 c, 73 d are used such that the two charge storagemeans 73 a, 73 b are connected to the xenon emission tube 71 a through acharge storage means changeover switch 76 a and an emission controlcircuit 72 a and the remaining two charge storage means 73 c, 73 d areconnected to the xenon emission tube 71 b through a charge storage meanschangeover switch 76 b and an emission control circuit 72 b. A xenonemission tube and optional charge storage means are combined to causeeach emission.

It is furthermore possible to use a construction where, as shown in FIG.31, only certain ones out of a plurality of xenon emission tubes areconnected to one charge storage means. In particular, the constructionmay comprise for example four xenon emission tubes 71 a, 71 b, 71 c, 71d and two charge storage means 73 a, 73 b, so that the xenon emissiontubes 71 a, 71 b are connected to the charge storage means 73 arespectively through emission control circuits 72 a, 72 b and a xenonemission tube changeover switch 80 a while the xenon emission tubes 71c, 71 d are connected to the charge storage means 73 b respectivelythrough emission control circuits 72 c, 72 d and a xenon emissionchangeover switch 80 b. One of the xenon emission tubes 71 a, 71 b andone of the xenon emission tubes 71 c, 71 d are selectively caused toemit.

Moreover, it is possible to use a construction where, as shown in FIG.32, any ones of xenon emission tubes out of a plurality of xenonemission tubes and any ones of charge storage means out of a pluralityof charge storage means can be selectively combined. In particular, theconstruction may comprise for example four xenon emission tubes 71 a, 71b, 71 c, 71 d and four charge storage means 73 a, 73 b, 73 c, 73 d suchthat each xenon emission tube is connected to the four charge storagemeans respectively through emission control circuits 72 a, 72 b, 72 c,72 d, an xenon emission tube changeover switch 80 and a charge storagemeans changeover switch 76. Each xenon emission tube can optionally andselectively be connected to any one of the charge storage means.

In addition, even in the case where combinations are specified andlimited of the plurality of xenon emission tubes and the plurality ofcharge storage means, it is possible to use a construction where, asshown in FIG. 33, three or more of such combinations are providedwithout defining those for use in a smaller emission and those for usein a larger emission so that combinations for smaller emission andlarger emission are selectively used respectively from the above threeor more combinations. In particular, the construction may comprise forexample four xenon emission tubes 71 a, 71 b, 71 c, 71 d and four chargestorage means 73 a, 73 b, 73 c, 73 d such that each xenon emission tubeis connected to each charge storage means respectively through emissioncontrol circuits 72 a, 72 b, 72 c, 72 d. The xenon emission tubes areselectively caused to emit by controlling the emission control circuitsby means of control signal from CPU.

A seventeenth embodiment will now be described. In the case ofgenerating two image pickup signals of different exposure amount byusing a strobe light, an emission amount of strobe light is adjusted asdescribed above, so as to achieve a predetermined emission amount ratio.In doing so, an emission amount based on the reflectance of an objectcan be obtained and the accuracy of an emission amount ratio be improvedby using a technique referred to as direct photometry where an actualemission amount is measured.

In particular, as shown in FIG. 34, there are provided an externalphotometric device 77 and an integrating circuit 78 for integratingquantity of light measured by the photometric device 77. Emission andintegration are started by control signal from CPU 8. The output ofphotometric integration at the integrating circuit 78 is inputted to anemission control circuit 72 to control timings of start and stop of anemission of a xenon emission tube 71. As another method, it is alsopossible that the integrated output of the integrating circuit 78 isinputted to CPU 8 and timings of start and stop of an emission of thexenon emission tube 71 are controlled in accordance with control signalfrom CPU 8.

A description will be given below by way of a flowchart shown in FIG. 35with respect to control operation of strobe emission in the seventeenthembodiment constructed as the above. First, control is effected of startof direct photometry of the external photometric device 77 (step 201).Next, control is effected of start of strobe emission of the xenonemission tube 71 (step 202), and an integrating operation of photometricvalue of the photometric device 77 is performed at the integratingcircuit 78 (step 203). An integrated voltage value corresponding to theintegrated photometric value is compared with a threshold voltagecorresponding to a preset emission amount to output a comparisondetection signal (step 204). Based on such output, a determination ismade as to whether or not the integrated voltage value exceeds thethreshold voltage (step 205). If the integrated voltage is determined asexceeding the threshold voltage, an emission stop signal is transmittedto the emission control circuit 72, where control of termination ofemission of the xenon emission tube 71 is effected (step 206) andcontrol is then effected of termination of direct photometry operationof the photometric device 77 (step 207).

Here, when an emission amount is thus controlled by measuring areflected light of an actual object as in the above, a problem occursthat accuracy is not quite adequate if such emission amount is to becontrolled to a small value. An eighteenth embodiment is made toeliminate this problem. An absolute value of emission amount can be setaccurately by separately providing a range finding device 79 forobtaining a distance information as shown in FIG. 36 so as to provideCPU 8 with the distance information. Specifically, a smaller emissioncan be controlled based on such distance information so that the smalleremission amount be set even more accurately. In particular, since anoptimum emission amount is experimentally determined in advance inaccordance with distance from the object, the attainment of distanceinformation makes it possible to accurately set an emission amount ofsmaller emission such as by means of control of emission time.

A nineteenth embodiment will now be described. In this embodiment, asshown in FIG. 37, the emission amount of strobe light at a first shot ofpicture taking is measured by means of direct photometry using anexternal photometric device 77 and an integrating circuit 78. Themeasured result is fed back to determine an emission amount of thesecond strobe light. It is thereby possible to effect an emission of thesecond strobe light at such emission amount that variance in emissionamount of the first strobe light is absorbed. In this way, too, accuracyin setting an emission amount ratio can be improved. The emission amountof the second strobe light in this case may be controlled by a timeduration of emission or a voltage at charge storage means or it may becontrolled by performing direct photometry by a photometric device in asimilar manner as the emission of the first strobe light.

The operation of the nineteenth embodiment will now be described in moredetail by way of a flowchart shown in FIG. 38. First, control iseffected of start of direct photometry by the external photometricdevice 77 (step 301). Next, control (dimming control) of the firststrobe emission by the xenon emission tube 71 is started and the strobeemission by the xenon emission tube 71 is terminated such as by controlof emission time of the xenon emission tube 71, or by detection of achange in the integrated voltage of the integrating circuit 78, or bydetection of a change in the charging voltage of main capacitor of thecharge storage means 73 (step 302). However, since the xenon tube 71possesses a surplus emission characteristic where an emission iscontinued for a short time period after an emission stop control, thedirect photometry by the photometric device 77 is continued further evenafter the emission stop control. A termination of emission is detectedat a point in time when the emission has substantially been terminatedupon an elapse of a time period set by a timer, or at a point in timewhen the integrated voltage at the integrating circuit 78 hassubstantially become constant, or at a point in time when the chargingvoltage of main capacitor of charge storage means has substantiallybecome constant (step 303). Next, control of termination of directphotometry operation of the photometric device 77 is effected (step304), and a final integrated voltage value of the integrating circuit isdetected (step 305). Next, based on such detected value, setting iseffected of the second strobe emission amount by the xenon emission tube(step 306), and control is effected of the second strobe emission by thexenon emission tube (step 307).

A twentieth embodiment will now be described. A technique has previouslybeen shown where emissions are caused by determining ratio between twoemission amounts so that the two strobe emission amounts at the twoshots of picture taking fall under an emission amount corresponding tothe capacitance of a single charge storage means. However, if, withoutsuch previous setting, an emission amount of the second time is setbased on a measurement of emission energy amount of the first time, theremaining amount of charge of the charge storage means may fall short ofthe set emission amount of the second emission, where a proper emissionamount ratio to be set cannot be achieved. In the present embodiment,even when such state has occurred, an exposure amount ratio by normallight and an emission amount ratio by strobe light can be set equal toeach other.

In this embodiment, as shown in FIG. 39, the remaining voltage of acharge storage means 73 after a first shot of picture taking is inputtedto CPU 8. If a second emission based on such voltage is smaller thanthat in accordance with a previously set emission amount ratio, thesecond emission is performed in its unmodified form and a secondexposure amount is controlled by a new exposure amount ratio based on anemission amount ratio to be set anew. Setting of the second exposureamount is effected by controlling the shutter 3 from CPU 8.Determination as to whether a remaining voltage of the charge storagemeans 73 is sufficient or not is made based on a correspondence databetween emission amounts and capacitor voltages which is providedinternally of CPU 8 in advance. If the remaining voltage of the chargestorage means is smaller than a capacitor voltage corresponding to thepreviously set second emission amount, it is determined as insufficient.Alternatively, a ratio of an energy amount corresponding to differencein voltages before and after the first emission to an energy amountcorresponding to an emission based on the remaining voltage (voltageafter the first emission) is obtained by measuring voltages of thecharge storage means 73 before and after the first emission and byinputting such value to CPU 8 to execute a predetermined arithmetic. Theenergy amount ratio and the emission amount ratio previously set by CPU8 are then compared with each other. It may be determined asinsufficient when the energy amount ratio is smaller.

The operation of the twentieth embodiment will now be described indetail by way of a flowchart shown in FIG. 40. At first, an emission iseffected of strobe light at a first shot of picture taking. A secondemission amount is set to an optional value which has previously beendetermined. Alternatively, it is computed based on an emission amount bydirect photometry of the first emission which has been performed byusing a photometric device (step 401). Next, the remaining value ofcharge of the charge storage means after the first emission is measuredsuch as by voltage output of the charge storage means (step 402), and adetermination is made as to whether or not an emission amountcorresponding to such remaining value is greater than the proper secondemission amount computed based on the value of the above directphotometry of the first time (step 403). Then, if the emission amountcorresponding to the remaining value is smaller than the second emissionamount computed based on the photometric value of the first time, anemission is caused at the second shot of picture taking so as to totallyuse the remaining value of the charge storage means. An emission amountratio in that case is set anew by a computation. Correspondingly to suchnewly set emission amount ratio, an exposure time such as by a means forshutting off light (mechanical shutter) at the second shot of picturetaking is adjusted so as to equalize the exposure amount ratio to theabove newly computed emission amount ratio (step 404) and a secondstrobe emission is effected (step 405). It should be noted that if, inthe above determination at step 403, the emission amount correspondingto the remaining value of the charge storage means is greater than asecond emission amount computed based on the photometric value of thefirst time, a second strobe emission is effected by the second emissionamount computed based on the photometric value of the first time in asimilar manner as the above described nineteenth embodiment.

It should be noted that, in the above described twentieth embodiment, acase is shown where an emission amount of strobe light at the secondshot of picture taking is computed based on an emission amount accordingto direct photometry of the first emission performed by using aphotometric device, i.e., only the emission at the first shot of picturetaking is actually measured and an emission at the second shot ofpicture taking is computed based on arithmetic. However, it is alsopossible to actually measure the first and second emissions so as toequivalently set an exposure amount ratio by normal light in accordancewith the actually measured emission amount ratio. In particular, a xenonemission tube is set to a predetermined emission amount ratio and iscaused to emit at a timing in the second half of the first shot ofpicture taking and at a timing in the first half of the second shot ofthe picture taking. The ratio between the two strobe emission amounts ismeasured by a photometric device. A photoelectric charge accumulatingtime of image pickup device at the second shot of picture taking is setin such a manner as to correspond to the actually measured emissionamount ratio. A further reduction is thereby possible of the effect dueto variance in a strobe emission amount.

Of the above described embodiments, in those embodiments including astep of actually measuring an emission amount of xenon emission tube,the emission amount of xenon emission tube can be measured not only bymeasurement using an external photometric device but also based on anactual measurement of voltage value of the charge storage means. In thiscase, it is not necessary to provide an external photometric device anda voltage measuring means of charging circuit of the charge storagemeans can be used in common. Further, of the above describedembodiments, in those embodiments including a step of controlling anemission amount of the xenon emission tube (dimming control), thedimming control in any of the cases can be performed by selectivelyusing control of emission time of the xenon emission tube, control ofdirect photometry by an external photometric device, or control based onvoltage measurement of the charge storage means.

Furthermore, of the above described embodiments, in those embodimentswhere at least one of the xenon emission tube and the charge storagemeans is consisting of a plurality of units, a single emission can becaused to emit by controlling a plurality of xenon emission tubes or aplurality of charge storage means and it is also possible to use again axenon emission tube or charge storage means which has been used in afirst emission.

What is claimed is:
 1. An electronic camera comprising: optical meansfor forming an optical image of object of picture taking; image pickupmeans for generating image pickup signals by taking picture andeffecting photoelectric conversion of an image of the object formed atthe optical means; flash emission means for illuminating the object;exposure condition designating means for designating exposure conditionsat said image pickup means; image pickup signal synthesizing means forsynthesizing two image pickup signals from two separate shots of picturetaking at said image pickup means by exposure conditions designated bythe exposure condition designating means; flash emission control meansfor controlling emission of said flash emission means in connection withthe exposure conditions with respect to each shot at the time of saidtwo shots of picture taking; and control means for controlling operationof each of the foregoing means, wherein said exposure conditiondesignating means includes one or both of electronic shutter means fordesirably controlling an exposure amount by controlling photoelectriccharge accumulation of said image pickup means and light shut off meansfor shutting off light from a light receiving surface of said imagepickup means, said control means controlling one or both of saidelectronic shutter means and said light shut off means, and said flashemission means to equalize between said two shots of picture taking anemission amount ratio by light from said flash emission means and anexposure amount ratio by normal light excluding the light from saidflash emission means.
 2. The electronic camera according to claim 1,wherein the exposure amount ratio by normal light of said two shots ofpicture taking is set by ratio of photoelectric charge accumulating timeof the two shots at said image pickup means.
 3. The electronic cameraaccording to claim 1, wherein said flash emission means comprises asingle charge storage means for accumulating emission energy of theflash emission means such that the total of emission amounts at the twoshots of picture taking of the flash emission means is set equal to orlower than the total emission energy of said single charge storagemeans.
 4. The electronic camera according to claim 1, wherein said flashemission means comprises a plurality of charge storage means differingfrom each other in capacitance value for accumulating emission energy ofthe flash emission means such that a full emission of the flash emissionmeans is caused at each of the two shots of picture taking byselectively using the plurality of charge storage means so as to make adifference in the total capacitance values to be respectively used. 5.The electronic camera according to claim 1, wherein said flash emissionmeans comprises a plurality of charge storage means for accumulatingemission energy of the flash emission means such that one picture takingis performed by a smaller emission based on a full emission using onesingle or a plurality of charge storage means and the other picturetaking is performed by a larger emission based on an emission underdimming control using the other single or plurality of charge storagemeans.
 6. The electronic camera according to claim 5, wherein saiddimming control is effected by control of emission time of said flashemission means.
 7. The electronic camera according to claim 5 furthercomprising a photometry means, said dimming control being effected basedon detection of a predetermined emission amount by direct photometry ofsaid photometry means.
 8. The electronic era according to claim 5,wherein said dimming control is effected based on measurement anddetection of a predetermined voltage at the charge storage means.
 9. Theelectronic camera according to claim 5, wherein, when dimming is to beeffected of the flash emission means at the second shot of picturetaking, an emission amount of light from the flash emission means at thefirst shot of picture taking is measured and an emission amount underdimming control of the flash emission means at the second shot is setbased on the measured emission amount so as to correspond to apreviously set emission amount ratio of the flash emission means betweenthe two shots of picture taking.
 10. The electronic camera according toclaim 9 further comprising a photometry means, the emission amount ofthe flash emission means at the first shot of picture taking beingmeasured by direct photometry of said photometry means.
 11. Theelectronic camera according to claim 9, wherein the emission amount ofthe flash emission means at the first shot of picture taking is obtainedby a voltage measurement at said charge storage means.
 12. Theelectronic camera according claim 1, wherein said flash emission meanscomprises a plurality of charge storage means for accumulating emissionenergy of the flash emission means such that one picture taking isperformed by a smaller emission based on an emission under dimmingcontrol using one single or plurality of charge storage means and theother picture taking is performed by a larger emission based on a fullemission using the other single or plurality of charge storage means.13. The electronic camera according to claim 12, wherein said dimmingcontrol is effected by control of emission time of said flash emissionmeans.
 14. The electronic camera according to claim 12 furthercomprising a photometry means, said dimming control being effected basedon detection of a predetermined emission amount by direct photometry ofsaid photometry means.
 15. The electronic camera according to claim 12,wherein said dimming control is effected based on measurement anddetection of a predetermined voltage at the charge storage means. 16.The electronic camera according to claim 12, wherein, when dimming is tobe effected of the flash emission means at the second shot of picturetaking, an emission amount of light from the flash emission means at thefirst shot of picture taking is measured and an emission amount underdimming control of the flash emission means at the second shot is setbased on the measured emission amount so as to correspond to apreviously set emission amount ratio of the flash emission means betweenthe two shots of picture taking.
 17. The electronic camera according toclaim 16 further comprising a photometry means, the emission amount ofthe flash emission means at the first shot of picture taking beingmeasured by direct photometry of said photometry means.
 18. Theelectronic camera according to claim 16, wherein the emission amount ofthe flash emission means at the first short of picture taking isobtained by a voltage measurement at said charge storage means.
 19. Theelectronic camera according to claim 1, wherein said flash emissionmeans includes at least one charge storage means for accumulatingemission energy of the flash emission means such that the two shots ofpicture taking are performed as illuminated by a smaller emission and alarger emission each based on an emission under dimming control.
 20. Theelectronic camera according to claim 19, wherein said dimming control iseffected by control of emission time of said flash emission means. 21.The electronic camera according to claim 19 further comprising aphotometry means, said dimming control being effected based on detectionof a predetermined-emission amount by direct photometry of saidphotometry means.
 22. The electronic camera according to claim 19,wherein said dimming control is effected based on measurement anddetection of a predetermined voltage at the charge storage means. 23.The electronic camera according to claim 19, wherein, when dimming is tobe effected of the flash emission means at the second shot of picturetaking, an emission amount of light from the flash emission means at thefirst shot of picture taking is measured and an emission amount underdimming control of the flash emission means at the second shot is setbased on the measured emission amount so as to correspond to apreviously set emission amount ratio of the flash emission means betweenthe two shots of picture taking.
 24. The electronic camera according toclaim 23 further comprising a photometry means, the emission amount ofthe flash emission means at the first shot of picture taking beingmeasured by direct photometry of said photometry means.
 25. Anelectronic camera according to claim 23, wherein the emission amount ofthe flash emission means at the first shot of picture taking is obtainedby a voltage measurement at said charge storage means.
 26. Theelectronic camera according to claim 1, wherein emission amounts of saidflash emission means are measured to obtain an emission amount ratiobased on the emission amount, the exposure amount ratio by normal lightbeing set as the same as the emission amount ratio.
 27. The electroniccamera according to claim 26, wherein the emission amount ratio isobtained by measuring an emission amount of the flash emission means atthe first shot of picture taking and by computing a second emissionamount by calculation based on the first emission amount.
 28. Theelectronic camera according to claim 27 further comprising a photometrymeans for measuring an emission amount of said flash emission meansbased on direct photometry by said photometry means.
 29. The electroniccamera according to claim 27, wherein an emission amount of said flashemission means is obtained by a voltage measurement at said chargestorage means.
 30. The electronic camera according to claim 26, whereinthe emission a mount ratio is obtained by measuring emission amounts ofthe flash emission means at the first and second shots of picturetaking.
 31. The electronic camera according to claim 30 furthercomprising a photometry means for measuring an emission amount of saidflash emission means based on direct photometry by said photometrymeans.
 32. The electronic camera according to claim 30, wherein anemission amount of said flash emission means is obtained by a voltagemeasurement at said charge storage means.
 33. The electronic cameraaccording to claim 26 further comprising a photometry means formeasuring an emission amount of said flash emission means based ondirect photometry by said photometry means.
 34. The electronic cameraaccording to claim 26, wherein an emission amount of said flash emissionmeans is obtained by a voltage measurement at said charge storage means.35. The electronic camera according to claim 1, wherein said flashemission means comprises one xenon emission tube and one charge storagemeans and is caused to emit at the two shots of picture taking by usingthe one xenon emission tube and the one charge storage means.
 36. Theelectronic camera according to claim 35, wherein said charge storagemeans comprises one main capacitor.
 37. The electronic camera accordingto claim 35, wherein said charge storage means comprises a plurality ofmain capacitors connected in parallel.
 38. The electronic cameraaccording to claim 1, wherein said flash emission means comprises onexenon emission tube, a plurality of charge storage means and chargestorage means switching means and is caused to emit at the two shots ofpicture taking by using the one xenon emission tube and at least one ofthe charge storage means switched and selected by the charge storagemeans switching means.
 39. The electronic camera according to claim 38,wherein said charge storage means comprises one main capacitor.
 40. Theelectronic camera according to claim 38, wherein said charge storagemeans comprises a plurality of main capacitors connected in parallel.41. The electronic camera according to claim 1, wherein said flashemission means comprises a plurality of xenon emission tubes, one chargestorage means and xenon emission tube switching means and is caused toemit at the two shots of picture taking by using at least one xenonemission tube switched and selected by said xenon emission tubeswitching means and the one charge storage means.
 42. The electroniccamera according to claim 41, wherein said charge storage meanscomprises one main capacitor.
 43. The electronic camera according toclaim 41, wherein said charge storage means comprises a plurality ofmain capacitors connected in parallel.
 44. The electronic cameraaccording to claim 1, wherein said flash emission means comprises aplurality of xenon emission tubes, a plurality of charge storage means,xenon emission tube switching means and charge storage means switchingmeans and is caused to emit at the two shots of picture taking by usingat least one xenon emission tube switched and selected by said xenonemission tube switching means and at least one charge storage meansswitched and selected by the charge storage means switching means. 45.The electronic camera according to claim 44, wherein said charge storagemeans comprises one main capacitor.
 46. The electronic camera accordingto claim 44, wherein said charge storage means comprises a plurality ofmain capacitors connected in parallel.
 47. The electronic cameraaccording to claim 1, wherein each emission of the flash emission meansat the two shots of picture taking is effected as a single emission. 48.The electronic camera according to claim 1, wherein the respectiveemissions of the flash emission means at the two shots of picture takingare effected either as one unit emission and a collection of a pluralityof times of unit emission or each as a collection of a plurality oftimes of unit emission.
 49. The electronic camera according to claim 1,wherein the respective emissions of the flash emission means at the twoshots of picture taking are effected as a smaller emission and a largeremission in that order.
 50. The electronic camera according to claim 1further comprising range finding means, an emission of said flashemission means being controlled to an optimum emission amountcorresponding to a distance information obtained by said range findingmeans.
 51. The electronic camera according to claim 50, wherein theemission to be controlled correspondingly to said distance informationis a smaller emission.
 52. The electronic camera according to claim 1further comprising pre-photometry means, an emission of said flashemission means being controlled by using a pre-photometry informationobtained by said pre-photometry means.
 53. The electronic cameraaccording to claim 52, wherein said pre-photometry means comprisesexternal photometry means.
 54. The electronic camera according to claim52, wherein said pre-photometry means is used in common as said imagepickup means.
 55. The electronic camera according to claim 1 furthercomprising pre-photometry means, an emission of said flash emissionmeans being controlled by using a pre-photometry information obtained atsaid pre-photometry means by causing a pre-emission of the flashemission means.
 56. The electronic camera according to claim 55, whereinsaid pre-photometry means comprises external photometry means.
 57. Theelectronic camera according to claim 55, wherein said pre-photometrymeans is used in common as said image pickup means.